Reconfigurable laser header

ABSTRACT

A reconfigurable laser header assembly, wherein either an n-doped laser substrate structure or a p-doped laser substrate structure can be properly biased, includes a header coupled to a modulated electric (AC) current source, a DC positive bias electric current source, and a DC negative electric current source. A laser is mounted relative to the header, the laser includes a base electric contact and a laser electric contact. An electrical conductor on the header includes first and second metalized regions in electrical connection with the base electric contact, wherein different ones of the modulated electric current source, the bias electric current source, and the DC negative electric current source can be electrically connected to the first metalized region, the second metalized region, and the laser electric contact to properly bias the laser regardless of whether the laser is an n-doped laser substrate structure or a p-doped laser substrate structure.

FIELD OF THE INVENTION

This invention relates to optical devices, and more particularly tooptical transmitters and/or optical receivers.

BACKGROUND OF THE INVENTION

Optical transponders include a combination of at least one opticaltransmitter and at least one optical receiver thereby providinginput/output functions in one device. The use of optical networks isincreasing. The bandwidth of the signals that optical transmitters cantransmit, and the bandwidth of the signals that optical receivers canreceive, is progressively increasing.

It is often important that optical devices such as optical transmittersand optical receivers be miniaturized. Miniaturization of opticaldevices is challenging. For example, positioning components closetogether may cause electromagnetic interference (EMI) of one opticaldevice (or component thereof) to interfere with another optical device(or component thereof). Additionally, the amount of heat that isgenerated (and thus has to be dissipated) is similar regardless of thesize of the component. As such, miniaturized optical devices have todissipate more heat for a given volume. As such, many designs employthermoelectric coolers to control thermal exposure of critical opticalelements such as lasers. Alternatively, they may have distinct heatgenerating devices (such as lasers and laser drivers within opticaltransmitters) separated by a considerable distance or in separatepackages. However the laser driver supplies a radio-frequency electricalsignal to the laser, and as such is located relatively close thereto.Spacing the components within an optical device may also result inelectrical conductors that extend between certain ones of thecomponents. An extended electrical conductor can act as a transmittingor receiving antenna of EMI or a parasitic element degrading highfrequency performance.

Optical transmitters and optical receivers typically include bothoptical and electronic (microwave) portions. In optical transmitters, anelectrical signal received and processed by the electronic portion isconverted into an optical signal and then transmitted over an opticalfiber cable. In optical receivers, an optical signal received over anoptical fiber cable is processed by the microwave portion and thentransmitted as an electrical signal.

A design challenge involves repairing, replacing, or updating anyoptical device that is mounted to a circuit board. It would be desiredto effectively replace one optical device (having both electronic andmechanical connections) by another optical device. Removal of an opticaldevice involves not only mechanical connections, but electricalconnections between the optical device and the circuit board must alsobe disconnected. To insert a replacement optical device, the applicableoptical device similarly is secured by providing a mechanical connectionas well as an electrical connection to the circuit board.

Materials play an important role in the design of optical devices. Thedevice packages that enclose optical transmitters or optical receiversmust adapt to a variety of mechanical, thermal, electrical, and opticalconditions. For instance, the different portions of the device packageare configured to withstand thermomechanical stresses, vibrations, andstrains that are applied by, e.g., outside forces to the device packagewhich houses the optical device. It is also required that differentparts of the optical device can tolerate different thermal expansionsthat would otherwise create excessive stresses or strains in the devicepackage resulting in optical instability. Thermal conditions also relateto the capability of operating successfully at a series of high or lowtemperatures, depending on the application. Additionally, the opticaldevice has to provide the optical and electrical functions for which itis designed. As such, the materials selected play an important role inallowing the optical device to perform its desired function.

In one aspect, it would be desired to provide an optical device that isdesigned to operate under the variety of thermal, mechanical, optical,and/or electrical conditions that the optical device will potentiallyencounter over its life. In another aspect, it would be desired toprovide a Faraday cage to limit the transmission of electromagneticinterference through a part of a device package case of an opticaltransmitter or optical receiver. In yet another aspect, it would bedesired to provide effective heat sinking from one or more heatgenerating components within an optical component. In yet anotheraspect, it would be desired to provide an effective surface mount tosecure an optical transmitter or optical receiver to a circuit board.

SUMMARY OF THE INVENTION

An aspect of the present invention is directed to a reconfigurable laserheader assembly that can be used to properly bias either an n-dopedlaser substrate structure or a p-doped laser substrate structure. Thereconfigurable laser header assembly includes a header that is coupledto a modulated electric (AC) current source, a (DC positive) biaselectric current source, and a DC negative electric current source. Theheader assembly also includes a laser mounted on the header, and anelectrical conductor formed from first and second metalized regions. Thelaser includes a base electric contact and a laser electric contact.Each of the first and second metalized regions is in electricalconnection with the base contact. Different ones of the modulatedelectric (AC) current source, the (DC positive) bias electric currentsource, and the DC negative electric current source can be electricallyconnected to the first and second metalized regions, and the laserelectric contact in a manner to properly bias the laser regardless ofwhether the laser is an n-doped laser substrate structure or a p-dopedlaser substrate structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute partof this specification, illustrate different embodiments of theinvention, and, together with the general description given above andthe detailed description given below, serve to explain features of theinvention.

FIG. 1 shows a perspective view of one embodiment of an opticaltransponder;

FIG. 2 shows a partially exploded view of the optical transponder ofFIG. 1 in which the cover is removed to show internal components of theoptical transponder including an optical transmitter and an opticalreceiver;

FIG. 3 shows a perspective view of the circuit board shown in FIG. 2,with the optical receiver shown as separated, and the opticaltransmitter shown as removed;

FIG. 4 shows a block diagram of one embodiment of an opticaltransponder;

FIG. 5 shows a top view of the optical receiver of the opticaltransponder shown in FIG. 2;

FIG. 6 shows a top view of the optical transmitter of the opticaltransponder shown in FIG. 2;

FIG. 7 shows a partially exploded view of the optical receiver of FIG.2;

FIGS. 8A-8B shows a partial exploded perspective view of an opticalreceiver subassembly;

FIG. 9 shows another exploded view of the ceramic wall portion in theoptical receiver including the baseplate and lead frame;

FIG. 10 shows a bottom view of the optical receiver with lead frameattached;

FIG. 11 shows a baseplate of the optical receiver;

FIG. 12 shows a top view of layer two of the optical device shown inFIG. 8;

FIG. 13 shows a bottom view of layer two of the optical device shown inFIG. 8;

FIG. 14 shows a top view of layer three of the optical device shown inFIG. 8;

FIG. 15 shows a top view of the lead frame mounted to assembled layersone, two, and three;

FIG. 16 shows a perspective exploded view of one embodiment of anoptical device using a surface mount adhesive pad;

FIG. 17A shows a side partial cross-sectional view taken through theoptical transmitter, the optical receiver, and a portion of the casingpackage as shown in FIG. 3.

FIG. 17B shows a side partial cross-sectional view taken through theoptical transmitter, the optical receiver, and a portion of the casingpackage as shown in FIG. 3;

FIG. 18 shows a side view of one embodiment of a surface mount thatsecures an optical device;

FIG. 19A shows a perspective view of one embodiment of an optical deviceremoval tool;

FIG. 19B shows a side view of the optical device removal tool being usedto remove an optical device from a circuit board;

FIG. 19C shows a top view of FIG. 19B;

FIG. 20A shows a cross-sectional view of one embodiment of a receiveroptical bench;

FIG. 20B shows a perspective view of the receiver optical bench shown inFIG. 20A;

FIG. 21 shows a perspective view of one embodiment of an opticaltransmitter, in which certain components are shown in an explodedposition;

FIG. 22A shows a top view of one embodiment of the components within anoptical transmitter;

FIG. 22B shows an expanded view of one embodiment of certain ones of thecomponents in the optical transmitter shown in FIG. 22A;

FIG. 22C shows an exploded view of another embodiment of certain ones ofthe components in the optical transmitter shown in FIG. 22A;

FIG. 22D shows a generalized circuit diagram of certain components ofthe optical transmitter as shown in FIGS. 22A, 22B, and 22C;

FIG. 23 shows a plot illustrative of the power out as a function of thecurrent for one embodiment of the laser of the optical transmitter ofFIGS. 22A and 22B at different temperatures;

FIG. 24 shows an exemplary plot of gain vs. frequency for one embodimentof the laser as used in the optical transmitter of FIGS. 22A and 22B atdifferent currents;

FIG. 25 shows a cross-sectional view of one exemplary embodiment of heattransfer through a series of vertically layered substrates;

FIG. 26 shows a heat transfer diagram similar to that shown in FIG. 15,except with the heat generation point located proximate to one of thevertical boundaries;

FIG. 27A shows a cross-sectional view of one embodiment of a header ortransmitter optical bench and a hybrid subassembly partially separatedby a vertically extending air trench formed therein, in which the airtrench defines a plurality of pedestals and which one of the pedestalssupports a laser and another one of the pedestals supports an additionalheat-generating component such as a laser driver;

FIG. 27B shows a side cross sectional view of one embodiment of thecomponents associated with an optical transponder including an opticaltransmitter, such as illustrated in FIG. 27A and an optical receiver;

FIG. 27C shows a side view, as taken through sectional lines 27—27 ofFIG. 27B;

FIG. 28 shows a top view of a laser and laser driver configuration forthe optical transmitter;

FIG. 29 shows a top view of another laser and laser driver configurationfor the optical transmitter;

FIG. 30 shows a top view of yet another laser and laser driverconfiguration for the optical transmitter;

FIG. 31 shows a side view of an n-doped laser substrate structure,including biasing;

FIG. 32 shows a side view of a p-doped laser substrate structure,including biasing;

FIG. 33A shows the reconfigurable laser header of the present invention,configured for a p-doped laser substrate structure;

FIG. 33B shows the reconfigurable laser header of the present invention,configured for a n-doped laser substrate structure;

FIG. 34 shows an eye diagram for one embodiment of laser operating in anoptical transmitter in one embodiment of the present invention;

FIG. 35 shows an optical isolator in accordance with the presentinvention;

FIG. 36 shows an optical isolator in accordance with a furtherembodiment of the present invention; and

FIG. 37 shows a cross-sectional view of the optical isolator shown inFIG. 36.

Throughout the figures, the same reference numerals and characters areused, unless otherwise stated, to denote like features, elements,components, or portions of the illustrated embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS I. Optical Transponder

One embodiment of optical transponder 100 that is included as part of anoptical/electronic network 102 is shown in FIG. 1. FIGS. 2 and 3 showdifferent views of the optical transponder 100 of FIG. 1 that includes acircuit board 108, a mateable electronic connector 140, an opticaltransmitter 112, and an optical receiver 114. The circuit board 108supports such exemplary optical devices 116 as the optical transmitter112 and the optical receiver 114. The optical transponder 100 performsthe transmitting, receiving, and other capabilities as described herein.

This disclosure describes a variety of aspects relating to the opticaltransponder 100. Certain general aspects of the Faraday cage, surfacemount components, matching materials characteristics, optical deviceremoval tool, and optical bench assembly as described herein areapplicable generically to the optical transmitter 112 or the opticalreceiver 114. Other aspects of the optical transponder relatespecifically to optical transmitter 112 but not typically the opticalreceiver 114. These aspects include effective laser, laser driver, andheader or optical bench configurations as described later in thespecification.

In this disclosure, the optical transmitter 112 and the optical receiver114 are each categorized as different embodiments of the optical device116. The optical transmitter 112 transmits optical signals over at leastone optical fiber cable 120. The optical receiver 114 receives opticalsignals over at least one of the optical fiber cables 120. The opticaltransponder 100 also includes a housing case 123. The housing case 123includes a casing 118 and a casing cover 117 that forms an enclosure119. The enclosure 119 encloses one or more optical devices 116 mountedwithin the enclosure.

Certain embodiments and views of portions of the optical transponder 100are shown in FIGS. 1-18, 20A, 20B, 21, 22, and 22A. FIG. 4 shows oneembodiment of a block diagram 800 for the optical transponder 100.The-optical transponder 100 provides the overall optical transmitter andoptical receiver functions. The optical transmitter 808 and opticalreceiver 810 represent the operational equivalents of similarly nameddevices that are described herein with respective references numbers 112and 114 in FIG. 2. The transponder block diagram 800 can be segmentedinto a transmitter portion 820 and receiver portion 822, with the clockand timing circuit 806 controlling certain timing aspects in both thetransmitter portion 820 and the receiver portion 822. The transmitterportion 820 includes an electrical multiplexer 802, a retiming circuit804, and an optical transmitter 808. The receiver portion 822 includesan optical receiver 810, a clock and data recovery circuit 812 and anelectrical demultiplexer 814.

The electrical multiplexer 802 receives a plurality of electrical inputsignals, and combines the plurality of electrical input signals into asingle multiplexed electrical signal. The retiming circuit 804 retimesthe multiplex electrical signal to allow it to be acted upon by theoptical transmitter 112. The optical transmitter 112 converts theelectrical signal (that typically is a multiplexed signal) into anoptical signal, which is configured to be transmitted over an opticalmedium such as an optical fiber cable or optical waveguide. The clockand timing circuit 806 controls the timing of the retiming circuit 804and the clock and data recovery circuit 812.

For the receiver portion, the optical receiver 810 receives an opticalinput signal over an optical fiber cable, or other optical medium suchas waveguide, and converts the signal into a multiplexed electricalsignal. The multiplex electrical signal is applied to the clock and datarecovery circuit 812 which (under the control of clock and timingcircuit 806) changes the multiplexed electrical signal output by theoptical receiver 810 into a form to be received by the electricaldemultiplexer 814. The electrical demultiplexer 814 acts to divide eachone of a plurality of electrical output signals that are combined in theelectrical multiplex signal. The optical/electronic network 102 furtherincludes a computer/communication device 104 and an optical network 106.The optical/electronic network 102 may be configured as a hybrid opticaland electronic network that allows a large number of end users tocommunicate. The general use of fiber optic networking is increasingwith optical networks such as SONET are gaining greater acceptance. Itis important to provide optical systems capable of transmitting and/orreceiving an ever-increasing bandwidth of data. SONET is presentlyprimarily configured as a backbone network protocol that provides forthe transmission of a large bandwidth of data over relatively largeoptical cables. One design challenge with optical networks is to providea so-called “first mile” optical protocol that transmits data betweeneach end user and the optical backbone.

The computer/communication device 104 shown in FIG. 1 is envisioned tobe an end-user terminal, such as a computer, network switch, orcommunications server computer. The computer/communication device 104can transmit and receive data in the form of video, audio, image, text,and/or any other known type of data. The optical network 106 isconfigured as, for example, the SONET network utilizing an optical cablethat can transmit a large bandwidth of data.

The optical fiber cables 120 extend through apertures 216 to connect totheir respective optical device 116. In one embodiment, the opticalfiber cable 120 is attached at the distal end (opposite from the endwhich is connected to the optical device 116) to an optical connector180. The optical connector 180 permits quick coupling and decoupling ofthe optical fiber cable 120 to an additional optical fiber cable oranother component of the remainder of the optical network 106. At leastone optical fiber cable 120 extends through the housing case 123 and isoperatively converted to an optical device 116.

Each optical device 116 is encased within, and includes a device packagecase 122 as shown in FIGS. 2, 3, 5, 6. The device package case 122 mayalso be referred to as a housing. The device package case 122 mayinclude one member, two members, or a plurality of members secured toeach other using such illustrative connecting techniques as anelectrically conductive adhesive, weld, soldering, and/or a mechanicalconnector or fastener. These connectors, as well as the materialsselected for the housing, are selected based upon thermal, mechanical,electrical, and optical considerations as described herein. Thedimensions of the package case 122 for each optical device 116 can bedesigned (considering miniaturization and other design criteria) basedlargely on the components of the optical subassembly located within thedevice package.

A variety of connections may be established between one of the opticaldevices 116 and some portion of the optical transponder 100 to securethe optical device 116 in position within the device package case 122.In one embodiment, the device package case 122 of the optical device 116can be secured to an attachment region 606, such as with the opticalreceiver 114 shown in FIGS. 2 and 3. In another embodiment, theattachment regions 606 may be formed directly in the housing case 123formed in the casing 118, such as with the optical transmitter 112 shownin FIGS. 2 and 3. In the latter embodiment, a cut-away region 602 isformed in circuit board 108 that permits the optical device 116 to bemounted securely to the attachment regions 606 located on the housingcase 123 formed in the casing 118. Heat sink fins 402 are arrangedacross a lower surface of the casing 118 as shown in FIGS. 1 and 3. Theheat sink fins 402 may have a substantially circular, rectangular, orother cross sectional configuration. In one embodiment, the lowermostsurface of the heat sink fins 402 is a plane that can be secured to somesurface to which the housing case 123 of the casing 118 is mounted.Securement fasteners 403 are used to mount the housing case package 123of the optical transponder 100 so the heat sink fins 402 are mounted ona mating surface. Such mounting of the heat sink fins 402 can enhanceheat transfer.

One embodiment of the device package case 122, shown in exploded view inFIG. 7, includes a baseplate 170, a backbone 204, a lid 206, and aceramic wall portion 208. The baseplate 170, the backbone 204, theceramic wall portion 208, and the lid 206 are each configured in such amanner as to remain within the overall dimensional limitations andmachinability requirements for the device package case 122. The “ceramicwall portion” 208, one embodiment of which is shown in greater detail inFIG. 8, is a structure including layered ceramic layers, certain of thelayers have applied metalization. Other embodiments of the devicepackage case 122 may include the components described relative to theembodiment of device package case 122 shown in FIG. 2. For example, thebackbone 204 and the ceramic wall portion 208 may be formed as a unitarymember in certain embodiments. The baseplate 170, the ceramic wallportion 208, and/or the backbone 204 may be formed as one member instill other embodiments.

The device package case 122, as shown in FIG. 8, is designed to containand protect the components located therewithin. The device package case122 encases an optical subassembly 210 within an enclosure formed in thedevice package case 122. The optical subassembly 210 is designed toperform the desired optical operation of the particular optical device116. In the optical transmitter 112, the optical subassembly 210 isconfigured as an optical transmitter subassembly whereas in the opticalreceiver 114, the optical subassembly 210 is configured as an opticalreceiver subassembly . The applicable optical subassembly 210 is affixedto the baseplate 170, although it can be affixed to other members in thedevice package case 122. FIG. 5 shows a top view of one embodiment ofoptical receiver 114 including the electrical lead interconnects 212.FIG. 6 shows a top view of one embodiment of optical transmitter 116including the electric lead interconnects 212. As shown in FIGS. 8 and 9and described below, the electric lead interconnects 212 in theembodiment of device-package case 122 can be connected to electrictraces that are formed on certain ceramic layers 172 and 174 of theceramic wall portion 208. In other embodiments, the electric leadinterconnects 212 themselves can partially extend through other portionsof the device package case 122 such as the lid 206, the baseplate 170,and/or the backbone 204. The first ceramic layer 172 of the ceramic wallportion 208 is mechanically and electrically secured to a lead frame 176that protects the electric lead interconnects 212 during transportation.The lead frame 176 is trimmed from the electric lead interconnects. Asshown in FIG. 9, the lead frame 176 includes a plurality of leadinterconnects.

Electric traces 214 are formed, in one embodiment, as metalized layerson one of the ceramic layers 172, as shown in FIG. 12. Metallic vias 218provide a connection between electric traces at different levels. Eachone of a plurality of electric traces 214 electrically connect to eitherthe electrical hybrid subassembly 110 and the optical subassembly 210.As such, the electric lead interconnects 212 electrically connect to theelectric hybrid subassembly 110 to optical subassembly 210 to providenecessary electric input/output thereto. The optical fiber cable 120extends through an aperture formed in the backbone 204. The backbone 204is attached to the baseplate 170, the lid 206, and the ceramic wallportion 208 to form the device package case 122. One embodiment includesa tungsten copper-based metal baseplate 170. The Invar-based backbone204 can be plated using gold or other suitable material.

The backbone 204 has a sufficiently large cross-sectional dimension toallow the aperture (not shown) to be machined therein. The aperture hasa dimension selected to retain and align the optical fiber cable 120relative to some component. Only certain materials can be drilled withsuch small diameter apertures as may be necessary precisely retain/alignthe optical fiber cable (e.g., about 0.0055″) to limit excessive motionand/or provide alignment of the optical fiber cable 120 within thedevice package case 122.

The connections between certain ones of the baseplate, the ceramic wallportion, the backbone, and the lid may be connected to each other usingbrazing, epoxy, and other attachment techniques depending on theparticular members being connected, the materials being used, and theoperating environment of the optical devices.

IA. Faraday Cage

One concern in the design of optical devices 116 is that electromagneticradiation can produce electromagnetic interference (EMI). The transferof EMI through a wall of a device package can be limited by use of aFaraday cage. Electromagnetic radiation includes not only electrical andelectronic radiation, but also photonic radiation (light, as used inoptical systems). EMI can destructively interfere with other digital oranalog signals such that the signals can be interpreted as providing anincorrect signal level indication.

Faraday cages 840 (one embodiment partially shown in FIG. 8) limit thetransmission of EMI generated by one device from interfering withanother device. Embodiments of the lid 206, the backbone 204, and thebaseplate 170 are each formed of material that is selected to limit thetransmission of EMI. As such, in the embodiment of device package case122 shown in FIGS. 2 and 8, the EMI would pass only through the basematerial (ceramic) of the ceramic wall portion 208.

In one embodiment, vias 218 formed as a plurality of laser-drilled holesthat extend within the ceramic wall portion 208 in the optical receiver114 as shown in FIGS. 13, 14, and 15, can be applied to opticaltransmitters 112 as well as optical receivers. The vias 218 continuefrom the lid 206 to the baseplate 170, shown in FIG. 7, to provide aground reference that can be reached at either location as well asprovide a portion of the Faraday cage 840, as described herein. The vias218 can also act as a ground plane for the RF trace.

Faraday cages 840 may be used alternatively with EMI receiving and/orEMI generating devices such as optical receivers 114 or opticaltransmitters 112. Faraday cages 840 in optical receivers 114 limit thetransmission of EMI from sources external to the device package case 122that would otherwise be received by the sensitive optical receiversubassembly 210 located within the device package case 122. Faradaycages 840 in optical transmitters 112 limit the transmission of EMI fromthe optical subassembly 210 that is located within the opticaltransmitter 112 to sensitive components (e.g., an adjacent opticalreceiver) located outside the device package case 122. The embodiment ofFaraday cage 840 shown in FIGS. 13 through 15 includes an arrangement ofvias 218 that extend about the periphery of the optical device 116. Thevias 218 are formed by punching through the layers of the ceramic wallportion 208 prior to lamination and cofiring. Alternatively, drillingcan be performed, e.g. using mechanical drilling, laser drilling, etc.The thickness and material of the layers of the ceramic wall portion maylargely dictate how the vias are formed. The vias 218 are shown assubstantially vertically extending in the embodiment of Faraday cage 840of FIG. 8, though they may also be angled or even extend substantiallyhorizontal. In certain embodiments, the vias 218 are metalized to takethe form of a series of substantially parallel metalized pillars. Thevias 218 may take the form of a series of parallel pillars formed of airvoids having a metal plated surface. Additionally, the vias 218 aretypically cylindrical, though they may be formed as tapered, curved, orsome other desired configuration.

The spacing between the adjacent vias 218 is selected to limittransmission of EMI, of the desired wavelengths, through the devicepackage case 122 to partially form the Faraday cage 840. The spacingdistance should be less than a quarter wavelength (λ/4) of the highestoperating frequency component requiring attenuation. The vias 218, assuch, extend in a direction substantially perpendicular to the baseplate170 and the lid 206. As shown in FIG. 8, the ceramic wall portion 208includes a plurality of cofired ceramic layers 302 (some of ceramiclayers may be metalized). Metalization layers are thus formed between orabove certain ones of the cofired ceramic layers 302 as shown in FIGS.10, 12, 13, and 15.

IB. Material Design Considerations For Ceramic Wall Portion

Material selection for the baseplate 170, the ceramic wall portion 208,the lid 206, and the backbone 204 is important since each component indevice package case 122 as shown in FIG. 7 provides the desired optical,mechanical, thermal, and electrical operation for optical devices. Thematerials in certain embodiments of portions of device package case 122may include Kovar and Invar. Certain components of the device packagecase 122 include parts made from different materials since differentportions of the device package case 122 have different designconsiderations and demands.

Different portions of the device package case 122 may be exposed todifferent temperatures based on the design, operation, and environmentof the optical device. One embodiment of device package includes avariety of components formed from different materials, wherein thematerials of each component is selected based on its operatingtemperature. Since different components have different temperatures, theselection of different materials having different coefficients ofexpansions allows each component to expand at similar rates. Therefore,if all components are formed from different materials, the differentportions may expand at different rates. Selecting materials for thedesign that have a similar rate of expansion thus limits the stressesand strains being created at certain device package locations.

Optical transmitters 112 and optical receivers 114 must/can be made morecompact as the operating frequency increases. Miniaturization thereforebecomes practical at higher operating frequency. Unfortunately, smallervolume devices (such as miniaturized device packages) tend to operate atsimilar temperatures as larger optical devices, and as such a similaramount of heat has to be dissipated over a smaller volume. As such, withminiaturization, material selection becomes more critical.

Longer electric lead interconnects 212 result in lower frequencyoperation. Conversely, smaller device packages and lead interconnectscan be designed for higher frequency operation. The designcharacteristics of the device package case 122 therefore become morecritical at increased frequencies, such as 40 GHz and above. Theselected material of the ceramic wall portion 208 provides matchedcharacteristics to 90 GHz and above. As packaging decreases indimension, transponders including optical transmitters 112 and/oroptical receivers 114 can be produced having an operating frequency of40 GHz, 90 GHz, and above. The frequencies of the optical devices 116described herein are illustrative, and will increase as technologiesimprove, and are not intended to be limiting in scope.

Integrated designs for optical transmitters 112 and/or optical receivers114 are also important for optical devices operating at the higheroperating frequencies, such as 40 GHz and above. As an example, a devicepackage case 122 may be integrated within another housing case 123and/or within the casing 118. The more integrated the components withinthe device package case 122 become, the smaller the overall dimension ofthe device package case 122 often become. Integration may involvephysically locating components close together so that the signals do nothave to travel a large distance, and thus the signals travel quickerbetween the components. The functionality and components that wereoriginally separated may in fact now be included in the same devicepackage case 122. This could increase the optical device response speedby eliminating walls and limiting distances between sub-components bymerging certain sub-components.

The electronic connector 140 can be integrated, in certain embodiments,into the device package case 122. The electronic connection 140 providesan interface that allows end users to connect their electronic devices(e.g., computers, phones, etc.) to the optical transponder 100. Thehousing case also includes an electrical multiplexer 250, a multiplexerpedestal 254, an electrical demultiplexer 252 and a demultiplexerpedestal 256. In one embodiment, the optical device 116 can be locatedproximate to the electronic mateable connector 140. Different devicepackage case designs (e.g., device packages designed by differentmanufacturers or designers) can be configured differently while stillachieving similar operational characteristics.

A microwave package may be fashioned with one or more co-planar lines,including the electric trace 214 that extends on top of (or within andthrough) the ceramic wall portion 208. The electric trace 214electrically connects with the optical device 116. The electric leadinterconnects 212 electrically connect to the electric trace 214. In oneembodiment, the electric lead interconnects 212 change from a co-planarline (with electric trace within the device package case 122) into acoaxial line (via and ground configuration that is located within theceramic wall portion). One or more ground planes (indicated as one ofthe combined electric lead interconnects 212 and electric traces 214)extend across the ceramic wall portion 208 from the interior of thedevice package case 122 to the lead interconnects on the exterior of thedevice package, and connects within the interior to the optical device116.

The RF electrical conductor structure (including microwave circuits) isused in many embodiments of optical receivers 114 and opticaltransmitters 112 that are miniaturized. This RF lead interconnectconfiguration allows the electric lead interconnects 212 to extenddirectly from a double micro-strip line so lead interconnects can bondto the outside of the device package case 122, which is desired when thedevice package is miniaturized. In these instances, the ceramic wallportion 208 extends around a large percentage of the periphery of thedevice package case 122 (in one embodiment, the entire peripheryexcluding the backbone 204). The ceramic wall portion 208 is configuredto allow for the inclusion of a large number of distinct electric leadinterconnects 212, electric traces 214, and vias 218 (that take the formof metalization layers that extend through the ceramic wall portion208).

Many components forming the device package case 122 are designed atleast partially based on thermal considerations. Aluminum nitridesubstrates (that may be used in headers, optical benches, hybridintegrated circuits, etc.) are fairly common in the industry. Thealuminum nitride substrates dissipate considerable heat from the variouselectrical and optical portions of the device package. This aluminumnitride substrate may be epoxied with electrically conductive epoxy,soldered, or brazed to the baseplate 170.

In one embodiment, the device package case 122 must achieve good thermalmanagement to dissipate the heat generated by a laser 1102, the laserdriver 1104, (shown in FIGS. 22A and 22B) or other heat generatingcomponents. For example, heat generated by the optical subassembly 210can be dissipated through the copper tungsten pedestal (202). Multipleelements can also interact to provide the thermal management includingthe optical subassembly 210, the electrically conductive epoxy, thebaseplate 202 (FIG. 21), and the adhesive pad 604 or 605 (FIG. 3). Theseelements act together to sink heat out of the critical components. Ifone of these items is missing or has poor thermal properties, thethermal properties of the whole system may degrade considerably. It isimportant that the substrate, and the associated attachment material,act as a heat sink to increase the thermal dissipation from the opticaldevice 116. In one embodiment, the chip located on the electrical hybridsubassembly 110 in the receiver includes a transimpedance amplifier(TIA).

The electrical hybrid subassembly 110 uses an aluminum nitride substrate(typically 10 to 15 mils thick) which is epoxied or soldered to thebaseplate 170 of the device package case 122. Certain embodiments of thebaseplate 170 and lid 206 may be formed from ceramic, and otherembodiments are formed from plated or solid metal. The optical assembly210 acts as a high purity, high definition substrate for

One embodiment of the ceramic wall portion 208 is formed from multipleceramic layers (including, for example, the layers 172 and 174), asshown in the embodiment of FIG. 9. Each ceramic layer 172 and 174 has tobe formed precisely. Each ceramic layer 172, 174 may be formed from aplurality (e.g., thirty or more) ceramic sublayers. To obtain thedesired operation, it is important to consider the electricalcharacteristics of the materials used to form the ceramic wall portion208. For instance, in one embodiment, cofired ceramics with very lowdielectric constants at 20 GHz and above are selected for the ceramiclayers 172 and 174 which increases the insulative electrical resistancebetween the various metalization layers.

The fabrication attributes of the ceramic must also be considered. Manycircuits require complex electrical connections between variousmetalized layers layered on the ceramic layers 172 and 174. Oneembodiment of the metalized layer pattern is shown in FIGS. 12 and 13with selected metalized vias 218 forming electrical connections betweenthe metalized layers. This requires that the ceramic and themetalization be capable of being fabricated to very close dimensionaltolerances. The metals used in the metalization process have to becompatible with the ceramic type and the method of processing. DuPontand Ferro are examples of companies that produce the types of ceramicsthat can be used in the ceramic layers 172 and 174 and the compatiblemetalization materials. An example of suitable ceramic material includeDuPont 943 Green Tape (a low temperature cofired dielectric) withcompatible DuPont HF500 series gold metal system.

The laminated configuration of the ceramic wall portion 208 combineswith the backbone 204, the baseplate 170 , and the lid 206 in theembodiment of device package 144 shown in FIG. 2 to provide a completerobust device package case 122 (and actually completes one embodiment ofthe Faraday cage). All of the components of the device package case 122acting together, and not any particular component thereof, thuscontribute to the robustness of the device package case 122.

The thermal aspects of the device package case 122 are also important.The baseplate 170 and the lid 206 may each be formed from a metallicmaterial such as Kovar, molybdenum, copper laminate, or copper tungsten.Copper and aluminum also have high thermal conductivity, but are noteffective because of their high coefficients of expansion. As such, thelid 206, the backbone 204, and the baseplate 170 become useful indissipating the heat from miniaturized optical devices. The specificbaseplate 170, lid 206, backbone 204, and/or ceramic wall portion 208materials described herein are illustrative in nature, and are notintended to be limiting in scope.

The appropriate combination of thermal conductivity and coefficient ofthermal expansion provides for a design balance for internal componentsof the device package case 122. The thermal conductivity appliesespecially to the baseplate 170 to allow transfer of heat from theinternal components to the outside of the device package. Matchedcoefficients of thermal expansion are required to limit the creation ofinternal stresses and strains as temperature of the optical devicevaries. Operationally, the lead frame 176 (also known as a tie bar)integrally supports the electric lead interconnects 212 during thetransport and assembly process. The lead frame 176 is trimmed off fromthe lead interconnects prior to use, and the lead interconnects are thenindividually formed. The electric lead interconnects 212 passing throughthe ceramic well portion 208, being metallic, have low electrical losscharacteristics preferably under 0.0004 dB/in and the interface betweenthe electric lead interconnects 212 and ceramic wall portion 208represents a low electrical loss region. Electrical signals travellingover the electric lead interconnects 212 can therefore propagate over along distance without excessive dissipation of the signal strength.Kovar or Invar can also be used for certain parts of the device packagecase 122.

ID. Surface Mounts

This portion describes certain embodiments of surface mounts 603 foroptical devices 116 (such as optical transmitters 112 and opticalreceivers 114) as shown in FIGS. 16 and 18. The surface mount 603includes the optical device 116, a receiver adhesive pad 605 or atransmitter adhesive pad 604, an attachment region 606 located on thecircuit board 108, and electrical connections 608 to which the electriclead interconnects 212 connect. The surface mount 603 acts tomechanically and electrically connect the optical device 116 to someportion of the device package case 122, as shown in FIG. 3 or somecomponent within the device package. Surface mounts 603 can beconfigured to take into account a variety of design considerations suchas thermal, electrical, and mechanical attachment and expansion, and/oroptical considerations.

An attachment region 606, on which the surface mount is mounted, may belocated on the circuit board 108, or alternatively as a separateplatform on the device package case 122 as shown in FIG. 3. The circuitboard 108 includes a substantially planar attachment region 606 that canbe adhered to by the adhesive pad 605. Mechanical considerations involvephysically securing the device package case 122 to the circuit board 108and/or the casing 118, so that the optical fiber cable 120 can besecured and operatively positioned for the optical device 116.Electrical considerations provide for the necessary electrical couplingof electrical signals from outside of the device package case 122 of theoptical device to the electrical hybrid subassembly 110 and opticalsubassembly 210 via the electric lead interconnects 212 and/or theelectric traces 214.

FIG. 17A shows a cross-sectional view of one embodiment of the mountingof the optical transmitter 112 and optical receiver 114 secured within aportion of the housing case 123. The optical receiver 114 is mounted bythe adhesive pad 605 to the circuit board 108. The circuit board 108includes a plurality of thermal vias 1650 that extend from theattachment region 606 downwardly through the vertical height of thecircuit board. The thermal vias 1650 transfer heat from the adhesive pad605 downwardly to the thermal pads 1725.

The optical transmitter 112 (in comparison to the optical receiver) isnot affixed relative to the circuit board 108. Instead the opticaltransmitter extends through the cut-away region 602 as shown in FIGS. 2and 3, and connects via the attachment pad 604 directly to the housing1606.

The housing case 123 includes a plurality of housings 1606, thatsupport, and transfer heat downwardly from, the optical receiver 114.Located below the housing 1606, across a large range of the bottom ofthe housing case 123, are the plurality of heat sink fins 402. Betweendifferent ones of the plurality of housings 1606 (that may support, forexample, the optical transmitter and the optical receiver) extends aplurality of connecting regions 1730 that additionally form part of thehousing case package 123. The vertical height of the connection region1730 is small compared to the vertical height of the housing 1606.

As such, the amount of heat that can be transferred from one housing1606 to another housing (e.g., such a plurality of housings may supportan optical receiver 114 and an optical transmitter 112), and therebylimit the amount of heat that flow between the housings. Since theamount of heat that can transfer between the different housing 1606 islimited by the dimension of the connecting region 1730, most of the heatthat transfers from the optical device 116 via the thermal vias 1650 tothe housing 1606 will continue downwardly to the heat sink fins 402. Thebase of the heat sink fins 402 are in contact with a surface that thehousing case 123 is secured to (the surface should be thermallyconductive) by securement fasteners 403, as shown in FIG. 2. As such,there is a thermal heat dissipation path from each device package case122 through the housing case 123 to a surface external of the devicepackage. This removal of heat from the optical device allows the opticaldevices to operate at cooler temperatures, thereby possibly enhancingthe operation thereof as described herein.

Another embodiment of mechanical connection that includes an attachmentregion 606 for each optical device is shown in FIG. 16. The attachmentregions 606 can be located on the circuit board 108 to provide separatesurface mounts 603 for each optical device 116. The components of theoptical transmitter 112 and the components of the optical receiver 114may, in certain embodiments, be located in the same device package case122. The components of the optical transmitter 112 and the opticalreceiver 114 include, respectively, electrooptical transmittercomponents and electrooptical receiver components.

One embodiment of the receiver adhesive pad 605 includes a copper padthat has a suitable adhesive coating 612 on both faces, as shown ingreater detail in FIGS. 16 and 18. Such receiver adhesive pad 604 ortransmitter adhesive pad 605 (or alternatively adhesive tape) aretypically commercially available having peelable paper affixed to bothfaces (not shown), wherein the paper can be peeled away leaving theadhesive coating exposed on the face of the adhesive pad 604 or 605. Inanother embodiment, the receiver adhesive pad 604 can be formed fromaluminum, that is as thermally conductive, though not as electricallyconductive, as copper.

In one embodiment, the transmitter adhesive pad 604 used to secure theoptical transmitter 112 is formed of different materials than thereceiver adhesive pad 605 that is used to secure an optical receiver114. Generally, receiver adhesive pads 605 that mount optical receivers114 may be configured to be electrically conductive (e.g., 0-0.20 ohm/sqinch) as well as thermally conductive (e.g., 0.5-6.0 watts/m-K.) Bycomparison, transmitter adhesive pads 604 that mount opticaltransmitters 112 may be designed to be electrically insulative (e.g.,10⁶ ohm/sq inch) and thermally conductive (e.g., 0.5-6.0 watts/m-K.)

The receiver adhesive pad 605 (including the adhesive) is electricallyconductive, and has good thermal characteristics. Copper, which formsthe adhesive pad 605 for optical receivers, has very good electricalthermal characteristics among the metals. Their coat adhesive is appliedto both planar faces of the adhesive pad 605 to affix the baseplate 170to the attachment region 606 on the circuit board 108. The thin coatadhesive, while in one embodiment not in itself electrically conductive,is sufficiently thin so electrical current can flow there through. Itmay be necessary to form the thin coat adhesive of a sufficientcross-sectional area to provide the necessary electrical current flow.The adhesive pads 604 and 605 can be cut relative to, or formed in, ashape to accommodate their particular optical device 116.

The height of the adhesive pad 604 and 605 are related to certainconfigurations of the optical device 116. As such, the height of theadhesive pad 604 or 605 determines any designed difference in verticalheight between the lower most surface of the receiver baseplate 170 ortransmitter baseplate 202 and the lowermost surface of the electric leadinterconnects 212.

In FIG. 16, a distance 720 represents the vertical distance between thelower most point of the electric lead interconnects 212 and the lowermost portion of the device package case 122. Similarly, a distance 722shows the vertical distance between the upper surface of the attachmentregion 606 and the upper surface of the electric contacts 608 on thecircuit board 108. The distance 722 is often zero since the electriccontacts 608 are often deposited at the same vertical height as theattachment region 606. Both distances 720 and 722 should be designedconsidering the prescribed thickness of the receiver adhesive pad 605 orthe transmitter adhesive pad 604.

If the distance 720 is greater than the distance 722, and if the devicepackage case 122 were attempted to be laid directly on the attachmentregion 606, then the lower-most portion of the electric leadinterconnects 212 would actually contact the electric contact 608thereby spacing the lower most surface of the device package case 122from the attachment region 606. The distances 720 and 722 compensate forvertical height of the adhesive pad 604 or 605. For example, assumingthat the adhesive pad 604 or 605 has a vertical height of 5 mils thecombined distances 720 and 722 would be selected to equal 5 mils.

By using optical devices that are configured so the difference indistances 720 and 722 match the prescribed height of the adhesive pad604 or 605; the electric lead interconnects 212 contact the electriccontact 608 when the device package case 122 is secured to the adhesivepad 604. Such contact of the electric lead interconnects 212 to theelectric contacts 608 allows for relative positioning therebetween thatenhances rapid and effective soldering of the electric leadinterconnects 212 to the electric contacts 608.

The distance 720 may change as the electric lead interconnects 212 areflexible to deflect under light loads. Such flexibility of the electriclead interconnects 212 may be desired so that the electric leadinterconnects 212 are physically biased against the electric contact 608as the device package case 122 is mounted to the attachment region 606using the adhesive pad 604. Such biasing may obviate the need forsoldering, or alternatively, to enhance the effectiveness of thesoldering to provide an effective electric contact. If the electric leadinterconnects 212 are flexible, however, then the thickness of the padis determined with distance 720 represented by the electric leadinterconnects 212 positioned in their respective deformed, or flexed,positions. The strength of the adhesive coating both the planar faces ofthe adhesive pad 604 or 605 has to be selected to be sufficient tosecure the device package case 122 so each of the electric leadinterconnects 212 is in its flexed position.

Compression of the adhesive pad 604 or 605 in the vertical direction islimited, since the adhesive pad has a limited spring constant and isrelatively thin (in one application, the pad is 4.4 mils thick). Theelectric lead interconnects 212 may have a certain amount of springbias. As the optical device 116 is mounted to the attachment region 606,the electric lead interconnects 212 will deform so the electric leadinterconnect 212 is biased against its respective electrical contact608. This spring bias connection is in lieu of, or in combination with,a soldered connection.

Once the optical transmitter 112 or optical receiver 114 is affixedusing the receiver adhesive pad 605 or the transmitter adhesive pad 604,a separate electrical contact 608 is established for each of theelectric lead interconnects 212 to the respective electric contact 608.In one embodiment, the electric lead interconnects 212 are soldered toelectrical contacts 608 formed in the circuit board 108 using localizedheat. To effect such soldering of the electric lead interconnects 212 tothe electric contact 608, the user could solder each electric leadinterconnect individually using that source equipment and soldermaterials, a laser, solder paste, or a variety of other solderingtechniques. Certain electrically conductive adhesives, glues, or epoxiessuch as Ablebond 967-1 may be used to mechanically secure andelectrically couple the electric lead interconnects 212 to theirrespective electrical contact 608.

Each electric lead interconnect 212 of the device package electricallyconnects to one electric contact 608 formed on the circuit board 108 asshown in FIG. 16. The electric contact 608 forms a portion of anelectronic mateable connector 140 as shown in FIGS. 2, 3, and 16. Afterthe device package case 122 is secured to the circuit board 108 usingtechniques described herein, the electric lead interconnects 212 areindividually attached to their respective electric contacts 608 locatedon the circuit board 108 by soldering techniques. The device packagecase 122 does not have to be heated during the soldering. Thetemperature of the optical device package case 122 thus can bemaintained within a relatively low desired range during the securing ofthe device package case 122 of the optical device 116 to the attachmentregion 606. It is desired to limit the heat applied to the devicepackage case 122 to maintain the operational characteristics of theoptical device 116. The surface mount 603 therefore satisfies certainmechanical, thermal, electrical, and optical needs for optical devices116. The design of the optical device 116 can be optimized to provideeffective operation as well as to provide desirable optical, thermal,mechanical, and electrical characteristics. Surface mounts 603 can beused regardless of the operating frequency of the particular opticaldevice 116.

IE. Optical Device Removal Tool

This section describes an optical device removal tool 900 for removingoptical devices secured by surface mounts 603. Mechanically, theadhesive pad 604 or 605 acts to secure the optical device 116 to theattachment region 606 of the circuit board 108. At some point in time,either during manufacture or service, it may be desired to remove theoptical device 116 (e.g., the optical transmitter 112 or the opticalreceiver 114) without damaging either the circuit board 108 or theoptical device 116. An optical device removal tool 900, as shown in FIG.19, can remove the optical device 116 secured with the adhesive pad 604or 605 to the attachment region 606. It may be desired to remove theoptical device 116 to replace, repair, upgrade, or modify the opticaldevice 116. It may be especially desirable to replace the opticaldevices for repairability and/or failure analysis, but additionally theoptical device removal tool 900 could be used for device upgrades, etc.

In time the adhesive in the adhesive pad 604 or 605 sets up, and itbecomes difficult to separate the optical device 116 from the circuitboard 108. The embodiment of the optical device removal tool 900 shownin FIG. 19 has the shape of a miniscule crow bar, a knife, or othershape that allows for a peeling or prying action. FIG. 19A shows aperspective view of one embodiment of optical device removal tool 900.The optical device removal tool 900 includes a peeling blade 902 and ahandle 904. The peeling blade 902 extends substantially perpendicular tothe handle 904 so as shown in FIG. 19C, the relatively small peelingblade, and not the handle, is proximate a footprint 940 in the congestedcircuit board 108 during removal of the optical device 116. There cannotbe any optical components positioned in the footprint that the peelingblade 902 is configured to operate within. The peeling blade 902, in oneembodiment, includes a plurality of fork portions 910 that surround acavity 912. The cavity extends into the handle 904, and is designed tofit around or straddle the leads 212 as shown in FIG. 19B and 19C, suchthat the fork portions 910 do not physically contact and damage thesensitive leads 212 during removal of the optical device 116. Theoptical device removal tool 900 may be several inches long so that theuser can securely grip the handle 904 of the tool during the peeling orprying action. However, the base dimension w1 of the fork portions 910is sufficiently small to fit on a correspondingly small area on theboard, such that use of the tool does not damage other devices on theboard during the prying action. The adhesive pads 604 or 605 as shown inFIG. 19B and 19C may be configured to have a smaller dimension than theoptical device 116, thereby permitting the fork portions 910 to fitwithin an overhang portion 920. Movement of the handle 904 as indicatedby arrow 922 thereby causes the fork to apply an upward force againstthe optical device 116 at the overhang portion 920, therefore prying theoptical device 116 away from the circuit board 108. The length of thehandle 904 is considerably larger than that of the fork 910, andtherefore as the force is applied to the handle 904, a pivot point 924is created causing an increased force to be applied to the for portions910.

Prior to use of the optical device removal tool 900 to remove theoptical device 116 from the circuit board 108, however, the solderconnections that mechanically and electrically secure the electric leadinterconnects 212 to the electrical contacts 608 on the circuit board108 have to be broken. To break the solder connections, the circuitboard 108 may be heated above the temperature at which the solder melts,but below the temperature that would cause any permanent damage toelectric lead interconnects 212 or to the device package case 122. Anytechnique that breaks the solder connections may be used. After thisbreaking of the solder, the electric lead interconnects 212 arephysically separated from the respective electrical contacts 608 towhich they have been soldered, adhered, or otherwise attached.

To break the mechanical attachment between the optical device 116 andthe attachment region 606 on the circuit board 108, the optical deviceremoval tool 900 first separates a small portion of the adhesive pad 604or 605 from the attachment region 606. Another knife tool, such as anexacto-knife, may then cut away a portion of the adhesive pad 604 or 605at a location on the adhesive pad that is separate from where theoptical device removal tool initially pried a portion of the attachmentpad 604 or 605 (e.g., on an exposed end). The prying action by theoptical device removal tool 900 acts to decrease the cutting forcenecessary to remove the optical device. The fork portions 910 opticaldevice removal tool 900 are designed to be very narrow so as not tointerfere with other components that are physically positioned adjacentto the removed optical device 116. Less force (and less resultantdamage) is necessary to remove an adhesive-attached planar object (suchas the optical device 116) affixed to a surface by peeling the planaradhesive at one edge than to shear the entire planar surface. Use of theoptical device removal tool 900 limits the risk of damage to the circuitboard 108 and optical device by shearing. With the peeling action, anedge portion of the adhesive pad 604 or 605 is peeled using the peelingblade 902. The optical device removal tool 900 can be used to pry theremainder of the optical device 116 from the circuit board 108. Afterremoval of the optical device 116 from the circuit board 108, theoptical device removal tool 900 can remove the adhesive pad 604 or 605from the circuit board 108 or the optical device 116 to which it remainsaffixed.

When an optical device 116 is peeled and pried from the circuit board108, certain forces are generated within both the optical device 116 andthe circuit board 108. These forces may include one or more torsionaland/or shear forces. The circuit board 108 and the optical device 116are both designed to have sufficient strength to resist any force thatwould be reasonably applied by the optical device removal tool 900during this removal process. The prying action should not be applied toa metalization region (such as the electric lead interconnects 212) thatcould be damaged. The forks 910 of the optical device removal tool 900thereby actually straddle the electric lead interconnects 212 duringoperation. Components are positioned so as not to be located close tothe electric lead interconnects 212 to limit the possibility of thecomponents being damaged during removal.

IF. Optical Bench

Many embodiments of optical subassemblies 210 include an optical bench1010, (one embodiment shown in FIGS. 20A and 20B). There are twoembodiments of optical bench described in this disclosure. A receiveroptical bench 1010 is described in this section that secures thoseoptical components that receive light, and convert the light intoelectrical energy as described relative to FIGS. 20A and 20B. Atransmitter optical bench, or header, 1108 as shown in FIGS. 21, 22A,22B, 22C is designed to support a laser (and other necessary components)that translate an electrical signal into light. The differentembodiments of optical bench 1010 and 1108 are illustrative in nature,and not limiting in scope, and illustrate that optical benches must beconfigured to encounter a wide variety of applications, conditions, andenvironments.

The receiver optical bench 1010 includes a V-groove 1012, a lens 1014, aturning mirror 1016, and a photodiode 1018. The receiver optical bench1010 acts like a fixture that securely holds and relativelypositions/aligns the various components 1012, 1014, 1016, and 1018within the device package case 122. The receiver optical bench 1010 addsa great deal of structural stability to the components supportedtherein. In the receiver optical bench 1010 shown in FIGS. 20A and 20B,light travels through the optical fiber cable 120 located in theV-groove 1012, exits the optical fiber cable 120, and is directed at thelens 1014 which focuses the light. The focused light is reflected offthe turning mirror feature 1016 integrated in the receiver optical bench1010. The light reflects from the turning mirror 1016 and strikes thephotodiode 1018 on the bottom side. The light is absorbed by thephotodiode 1018, and is converted into an electrical signal.

The photodiode 1018 is affixed to the receiver optical bench 1010. Inone embodiment, the photodiode 1018 is secured above the turning mirrorfeature 1016 by, e.g., soldering. In one embodiment the photodiode 1018is bonded directly to the receiver optical bench 0110. The lens 1014 ispositioned in a cavity 2060 formed in the receiver optical bench 1010.The optical fiber cable 120 is inserted in the V-groove 1012 duringassembly. The positioning of the different components within thereceiver optical bench 1010 produce the optical alignment. Thephotodiode 1018 and the optical fiber cable 120 are positionedaccurately. In one receiver optical bench 1010 application, opticalfiber cable arrays can be spaced using receiver optical benches 1010.One embodiment of a receiver optical bench 1010 can be produced as oneintegral block of material such as silicon, instead of multiple blocks.The one embodiment of the receiver optical bench 1010 is made primarilyof silicon in which the turning mirror feature 1016 is coated with ametalization material to provide a reflective surface. Chrome-nickel,gold, etc., or alternatively any optically reflective metalized materialthat can be coated could be used for the metalization of the turningmirror 1016.

Precise dimensional features and accuracy, low coefficients of thermalexpansion, and good thermal conductivity are desired attributes foroptical benches. As such, the embodiment of the receiver optical bench1010 or transmitter optical bench 1108 uses silicon which isstructurally robust, in ready supply, can be accurately etched andmachined, can be patterned with metalization, and is inexpensive.V-grooves 1012 may be formed in the silicon using anisotropic etching inwhich the material of the receiver optical bench 1010 or header ortransmitter optical bench 1108 is etched at different rates alongdifferent directions, depending on the crystalline structure of thematerial (such as silicon). Anisotropic etching can produce etchedsurfaces that are exceptionally smooth and planar. Various othertechniques can be used to shape silicon and other semiconductors for anreceiver optical bench 1010 or the transmitter optical bench 1108. Forexample, a silicon carbide cutting tool may be used to cut the receiveroptical bench 1010 or the transmitter optical bench 1108, or certainetching techniques may be applied.

The photodiode 1018 straddles the turning mirror feature 1016 formed inthe receiver optical bench 1010. The photodiode 1018 is preferablyrear-illuminated to enhance performance, but can be front-illuminated.Rear-illuminated photodiodes 1018 are preferred for superiorresponsivities (micro-amps of current generated when subject to a givenquantity of light energy in watts) and lower capacitance (fasterresponse time) of the photodiode 1018. An amplifier 1022 is inelectrical connection with the photodiode 1018 to amplify the signalproduced by the photodiode 1018. The photodiode 1018 and the amplifier1022 are located close together to minimize signal transmissiondistance.

A native oxide can be grown upon the surface of the etched silicon toprovide an insulative passivation layer upon which metalization can bedeposited for the purposed of circuit interconnection. Electric traces,shown in FIG. 22 may, or may not be, formed on the material of thereceiver optical bench 1010 or the transmitter optical bench 1108.Silicon can be doped for different bulk resistivity: very highresistivity (greater than 10,000 ohms per square), high resistivity(greater than 1000 ohms per square), low resistivity (greater than 10ohms per square but less than 1000 ohms per square) and pure intrinsicsilicon (less than 10 ohms per square). If the silicon substratestructure is a base for simple electrical interconnections, lowresistivity silicon may be used. Silicon material with a relatively lowresistivity, under most conditions, would be too lossy to provide goodhigh frequency electrical conductivity. In the current embodiment, thereceiver optical bench 1010 or transmitter optical bench 1108 does notrely on running high frequency electric traces 214 on the silicon.However, in another embodiment, high resistivity or very highresistivity silicon material could be used and with a properconfiguration could be made to function properly.

The receiver optical bench can be configured as single blocks oralternatively from multiple blocks. Multiple ones of the blocks can befabricated to increase heat dissipation, such as where the receiveroptical bench supports a laser. The receiver optical bench 1010 ortransmitter optical bench 1108 may be fabricated from a plurality ofassembled “building block” parts that are fabricated to precisedimensional tolerances. Silicon is most adaptable for receiver opticalbench 1010 or transmitter optical bench 1108 processing due to itscapability of being machined and etched to very close tolerances. Thealignment of the components within the optical benches 1010 or 1108 canbe relatively simple, and can even be performed passively. An assembledoptical bench can use precision etching to provide component mountinglocations. Active alignment of optical benches 1010 or 1108 may requirethe biasing of the optical diode (the laser or the photodiode),monitoring of the output of the optical device based on the biasing theoptical diode, and positioning the fiber or lens system or other opticalelements to optimize optical performance. Passive alignment of opticalbenches 1010 or 1108 requires the accurate placement of the componentswithout application of any bias to the laser or the photodiode. In oneembodiment using the receiver optical bench 1010, such passive alignmentoccurs solely by physical placement of a first set of known features onthe optical diode relative to a second set of features on the siliconbench. Such optical fibers 120 may be placed into the v-groove 1012using passive placement techniques and subsequently aligned passively oractively as described herein. They may then be secured in place usinglaser welding, soldering and/or adhesives following passive alignment oractive alignment.

The use of the optical benches 1010 increases the performancecapabilities of the optical device. There are component and structuralvariations between an optical bench to be used for the opticaltransmitter 112 and an optical bench to be used for the optical receiver114. For example, the optical bench used for an optical receiver 114primarily supports the photodiode. Similarly, the optical bench used foran optical transmitter supports a laser and/or a feedback photodiodemonitor as described herein that is not included in the receiver opticalbench 1010.

An aluminum nitride or similar substrate material 1105 of FIG. 21mounted on the baseplate 202, may house electronic components. Thealuminum nitride substrate and the baseplate 202 are both thermallyconductive, and thus provide for heat dissipation from the electroniccomponents. Other materials can be selected to house the electroniccomponents.

The thermal effectiveness of epoxies or adhesives are limited especiallyif the epoxy is more than e.g., one-thousandth of an inch thick. Assuch, the thickness of the epoxy may be limited to below such aprescribed value. The aluminum nitride substrate and the epoxy layer areboth selected to be thermally conductive.

This disclosure has been directed to a variety of aspects of opticaldevice 116 including that apply to an optical transmitter 112, anoptical receiver 114, or an optical transponder 100. For example, theFaraday cage 840 configuration shown in FIG. 8 can be applied to eitheran optical receiver 114 or an optical transmitter 112. Similarly, thesurface mount 602 described herein can be applied to the device packagecase 122 for either an optical transmitter 112 or an optical receiver114. Additionally, the general configuration of the optical device 116including the lid 206, the baseplate 170, the backbone 204, and theceramic wall portion 208 may be applied to either an optical transmitter112 or an optical receiver 114. The optical bench 1010 may also beapplied to either an optical transmitter or an optical receiver. Forinstance, FIGS. 20A and 20B show an optical bench for an opticalreceiver configuration. By comparison, the header or transmitter opticalbench 1108 shown in FIGS. 22A and 22B may be considered as an opticalbench for an optical transmitter.

II. Optical Transmitter

This segment of the disclosure is directed particularly to certainaspects and embodiments of optical devices 116 configured as opticaltransmitters 112 that include a laser 1102 described particularlyrelative to FIGS. 22B, 27B and 27C. One aspect relates to the componentsthat are located on the header or transmitter optical bench 1108 thatsupport the laser 1102. One aspect relates to sinking heat away from thelaser 1102 within the optical transmitter 112. Another aspect relates toforming air trenches between a header or transmitter optical bench 1108that support the laser 1102 and a hybrid subassembly 1105 that supportsa laser driver 1104. Yet another aspect relates to variousconfigurations of coplanar waveguides that transmit an electric signalfrom the laser driver 1104 to the laser 1102. Another aspect relates tothe configuration of optical isolators. These aspects are describedbelow.

IIA. Optical Transmitter Configuration

The embodiment of optical transmitter 112 shown in FIGS. 21, 22A. 22B,and 22C includes the header or transmitter optical bench 1108; thehybrid subassembly 1105; a lens 1112; a second lens 1119; an isolatorassembly 1129; and a co-planar waveguide 1126. The header or transmitteroptical bench 1108 supports and provides a heat sink for the laser 1102.The hybrid subassembly 1105 supports and provides circuitry for thelaser driver 1104. The optical isolator assembly 1129 is located betweenthe two lenses 1112 and 1119 and prevents reflections from the opticalnetwork 106 from re-entering the laser and degrading opticalperformance. The lens 1112 colummates the coherent light emitted fromthe laser and lens 1119 refocusses the light onto the optical fibercable 120.

The laser driver 1104 imparts sufficient electrical energy to a lasingmedium in the laser 1102 to cause the laser to generate coherent lightby lasing action. The laser 1102, the laser driver 1104, and certainother components will generate a considerable amount of heat during thelasing operation within the optical transmitter 112. Therefore, theheader or transmitter optical bench 1108, the hybrid subassembly 1105,and certain other components of and within the device package 122 caseof the optical transmitter 112 (and housing case 123 of the opticaltransponder 102) are configured to dissipate thermal energy throughpassive conductive heat sinking. Such passive conductive heat sinkingdissipates heat from the laser 1102 and the laser driver 1104 throughthe device package case 122 and the housing case package 123.

There are a variety of power sources that supply power to the laser 1104including alternating current (AC) electric input and direct current(DC) electric input. The hybrid subassembly 1105 supports the laserdriver 1104. Additionally, the hybrid subassembly 1105 supplies DC andRF electrical signals to the header or transmitter optical bench 1108,and eventually to the laser 1102. The arrow 1150 shown in FIG. 22B and22C shows the path of current to provide the positive DC electric inputto the laser. The arrow 1150 passes through an electric contact 1149 anda pair of inductors 1118 and 1121 (which as an RF filter) to provide theDC electric input to the laser 1104. In one embodiment, an AC signal(e.g., R.F., microwave, etc.) generated by the laser driver 1104 isdirected at a coplanar waveguide 1126. The arrow 1152 shown in FIG. 22Band 22C shows the path of the AC electric current through the componentsto provide the AC electric input to the laser. The arrow 1152 passesthrough the laser driver 1104 and the coplanar waveguide 1126 to providethe AC signal to the laser 1104. The combined AC and DC signals arecapable of applying sufficient electrical energy at the laser 1102wherein the laser 1102 lases and emits light.

The header or transmitter optical bench 1108 is densely populated withsuch passive electric components as the inductors 1118 and 1121, theco-planar waveguide 1126 and an integrated matching resistor 1124. Suchdense population limits the electrical signal transmission period to thelaser.

The laser is capable of emitting light from both the front facet (to theright of the laser 1104 shown in FIGS. 22A and 22C) and the backsidefacet (to the left of the laser as shown in FIGS. 22A and 22C). Theforward direction and the rearward direction are substantially colinearand follow a lasing axis. Light emitted by the laser 1102 in a forwarddirection is directed towards the lens 1112. In one embodiment, thelaser driver 1104 is oriented so its projected energy is substantiallyparallel to the lasing axis of the laser 1102. Light emitted rearwardfrom the laser is directed to the photomonitor 1114. The AC amplitudeand the positive DC bias applied to laser is varied based on the outputof photomonitor 1114, and the temperature sensor 1119 described below.The photomonitor 1114 and the temperature sensor 1119 are activecomponents located on the header or transmitter optical bench 1108, butthey are not high bandwidth components. RF components mounted on theheader or transmitter optical bench 1108 may include, e.g., one or moreinductor coils 1118, 1121, co-planer waveguide 1126 and/or laser 1102.The header or transmitter optical bench 1108 may be made of a materialsuch as silicon, sapphire, aluminum nitride, diamond or other materialthat allows for the desired physical attributes: ease of fabrication andmetalization patterning, low thermal expansion, high heat transfer,precise physical geometries, and suitable electrical properties.Features, such as V-grooves and metalization features may be preciselyformed on, and in between, the header or transmitter optical bench 1108by etching or other means a previously described. The laser 1102 ispositioned relative to the lens 1112 and affixed onto the header ortransmitter optical bench 1108.

Due to the relative position of the laser 1102 and the lens 1112, lightemitted from the front of the laser 1102 is directed toward the lens1112 and is collimated by the lens 1112. Light passes through theoptical isolator assembly 1129. After light passes through the isolatorassembly 1129, the light passes through a second lens 1119 where thelight is refocused and coupled into the optical fiber cable 120 andhence is transmitted over the optical fiber cable 120. The positions andcharacteristics of lenses 1112 and 1119 are selected based on thedispersion angles of the laser 1102 and the desired focal distance forthe fiber 120. The header or transmitter optical bench 1108 componentsare precisely positioned relative to other optical transmitter 112components to provide acceptable alignment of the light paths and deviceoperation.

Different embodiments of the laser 1102 include a distributed feedback(DFB) laser, a Fabry-Perot (FP) laser, or other similar type ofsemiconductor-based laser. The semiconductor-based laser 1102 may bearranged having a low profile (the laser 1102 is relatively short),therefore the device package case 122 containing the laser 1102 can thusalso be relatively small. The laser driver 1104 is mounted on the hybridsubassembly 1105 of the optical transmitter 112 to provide an effectivemodulation source. The photomonitor 1114 is mounted on the header ortransmitter optical bench 1108 behind the laser 1102 in the embodimentshown in FIGS. 22B and 22C.

IIB. Coplanar Waveguide

The coplanar waveguide 1126 transmits the AC (e.g., RF) signal from thelaser driver 1104 to the laser 1102. The coplanar waveguide 1126 thusextends from the laser driver mounted on the hybrid subassembly 1105 tothe laser 1102 mounted on the header or transmitter optical bench 1108.The coplanar waveguide 1126 may be considered as not acting as awaveguide in an optical sense, but instead as a waveguide in the AC ormicrowave sense since the coplanar waveguide can transmit thehigh-frequency signals from the laser driver 1104 to the laser 1102 withlow electrical loss and low electrical reflections. The coplanarwaveguide 1126 is configured to adapt to the relative positions of thelaser driver 1104 and the laser 1102. The coplanar waveguide 1126 may,thus, be straight, curved, angled, or a variety of differentconfigurations. It is desired to minimize the electric transmission lossthrough the coplanar waveguide 1126. Typical high speed (radiofrequency) transmission line theory can be used to compute the requiredcharacteristic geometries required for a selected substrate material.Software programs exist to assist in the computation and analysis ofthese characteristic geometries. Another technique that minimizes thetransmission loss is to make all transitions and turns of the coplanarwaveguide 1126 as gradual as possible. For example, jagged surfaces,sharp angles and radical constrictions should be avoided in thewaveguide surface 2252 of the coplanar waveguide. The coplanar waveguide1126 includes a support substrate 2254, the waveguide surface 1126, apair of electric insulator strips 2250 that define respective opposedoutward return field planes of the waveguide surface 2252, a pair ofelectric contact locations 2252, and a plurality of ground vias 2256.The coplanar waveguide 1126 has different configurations depending onthe relative location of the laser driver 1104 and the laser 1102. Thereare a variety of coplanar waveguide designs that are described herein.In FIG. 22B, for example, the coplanar waveguide 1126 curves 90 degreesin a horizontal plane. The curves surface 1110 has a full radius shapeto minimize electrical reflections of the electric energy provided bythe laser driver 1104 at the laser. Alternatively, an arc or parabolicshape could be used for alternate configurations. The embodiment of thecoplanar waveguide 1126 shown in FIG. 77B is angled through 90 degreesto accomplish multiple features. The 90 degree curve allows thetransmission of an AC signal from the laser driver 1104 along the pathindicated by arrow 1152 to the laser 1102 to be directed on a low-losselement from the laser driver 1104 to reach the laser 1102 with aminimum signal perturbation. The channeling within the coplanarwaveguide 1126 keeps all the high frequency signals intact, robust, andvery pure into the laser 1102. Additionally, the 90 degree curve allowsthe laser driver 1104 to be positioned on an opposed side of a verticalair trench 1134 from the laser 1102. This separation of the laser 1102from the laser driver 1104 by the vertical air trench 1134 allows thelaser to operate cooler, as described herein. Additionally, the selectedgeometry permits integration of a matching resistor 1124 into theco-planar waveguide at a location very close to the laser 1102. Thematching resistor 1124 is mounted adjacent to the laser 1102 creating amatched circuit based on the resistance of the matching resistor 1124and the laser 1102.

In FIG. 22C, the coplanar waveguide is straight. FIGS. 28 and 30 showfurther embodiments of coplanar waveguides. In the embodiment of FIG.28, the laser driver 1104 and laser 1102 are positioned at the centersof their respective substrates. In some applications, positioning oflaser 1102 and laser driver 1104 at the centers of the header 1108 andhybrid subassembly 1105, respectively, may result in improved heatsinking.

The embodiment of coplanar waveguide 1126 shown in FIGS. 22A and 22B hasa 90-degree bend within a substantially horizontal plane as shown by1110 that directs energy emitted from the laser driver 1104 to the laser1102. The angle from surface 1110 may be as desired to allow the laserdriver 1104 to be positioned, as desired, relative to the laser 1102.The coplanar waveguide 1126 can be manufactured separately from the restof the header or transmitter optical bench 1108 from less expensive,precision materials such as alumina, and then integrated as a separateunit on the header or transmitter optical bench 1108. Alternatively, theheader or transmitter optical bench 1108 and the coplanar waveguide 1126can be formed as an integrated device where the discrete coplanarwaveguide effectively is not necessary.

IIC. Header and Hybrid Configuration

The hybrid subassembly 1105 is discrete and includes an aluminum nitridesubstrate that acts as part of its heat dissipation system. Aluminumnitride is a very good thermal conductor. Beryllium oxide, siliconcarbide, diamond or sapphire could alternatively be used. In certainembodiments, portions of the header or transmitter optical bench 1108and the hybrid subassembly 1105 are made of alumina. Alumina isrelatively inexpensive and has very good microwave properties but poorthermal properties. The header or transmitter optical bench 1108 istypically, however, formed from silicon. Such silicon may, or may not,be a semiconductor based on the doping levels applied to the silicon.

The material and configuration of the header or transmitter opticalbench 1108 has a bearing on the laser 1102 operation. The input from thelaser driver 1104 is located proximate to the laser 1102. The opticaltransmitter 112 may have RF electric lead interconnects 212 extendingalong one side of the device package case 122 and DC electric leadinterconnects 212 extending from another side of the device package case122 to limit a direct lead interconnect interference that mightotherwise provide considerable electromagnetic interference (EMI). Also,the electric traces 214 in the device package case 122 have to be routedto where they can be used. Therefore, the electric traces 214 can berelatively long in cases where the device package case 122 is relativelylarge or there are multiple non-separated device packages. Long electrictraces can act as antennae that generate considerable EMI. With aminiaturized device package case 122 as shown in FIGS. 21 and 22, thelength of the electric traces 214 included within the device packagecase 122 (and any associated EMI) is limited. The high-frequency signalscan thus be driven from the side of the optical transmitter 112, throughcontrolled impedance traces, through the laser driver 1104, by means ofa co-planar waveguide 1126 and to the laser 1102 without signalperturbation or degrading irradiation.

The header or transmitter optical bench 1108 can be designed of either alow-resistivity silicon (less than 1000 ohms per square and greater than10 ohms per square) or a high-resistivity silicon (greater than 1000ohms per square) or very high resistivity silicon (greater than 10,000ohms per square). High-resistivity silicon is more expensive thanlow-resistivity silicon due to controlled doping processes and becauseof the relatively low availability in the marketplace. However, use ofthe high-resistivity silicon allows the co-planar waveguide 1126 and thematching resistor 1124 to be integrally patterned on the header ortransmitter optical bench 1108. The matching resistor 1124 has animpedance that matches the impedance of the laser. The matching resistorshould be located in close proximity to the laser 1102. In oneembodiment, a plurality of ribbon bonds 1128 (as shown in the embodimentof FIGS. 22A and 22B) electrically interconnect the laser driver 1104 tothe hybrid subassembly 1105. The approximate size of one embodiment ofribbon bond 1128 is 10 mils by 3 mils by 0.5 mils thick.

The laser 1102, the lens 1112, the optical isolator assembly 1129, andthe lens 1119 may be arranged substantially axially to partially definethe optical path through the optical transmitter 112.

In one embodiment, a temperature sensor 1130 is located on the header ortransmitter optical bench 1108 to provide real time temperaturemonitoring of the laser 1102. The temperature sensor 1130 is locatedclose to the laser 1102 , as a result there is little thermal impedancebetween the two. In this embodiment, the header or optical bench 1108has an upper surface that defines a plane on which the is laser mounted.The axis of light emitted from the laser 1102 is parallel to the planeof the header or optical bench 1108. The temperature of the laser isobtained from the output of the temperature sensor 1130 withoutapplication of an offset to the temperature sensor output. An effectiveclosed loop management of the laser positive DC bias electric currentsource is therefore established that provides output power control usingfeedback based on predefined laser operating parameters at knowntemperatures. In one embodiment, the header or transmitter optical bench1108 is about 5 mm or less in width, and the temperature sensor 1130 ispositioned within 2.5 mm of the laser 1102. In a further embodiment, thetemperature sensor 1130 is positioned within 1 mm of the laser 1102.

In the embodiment of the header or transmitter optical bench 1108 shownin FIGS. 21, 22A, 22B, and 22C, there are a number of components mountedon the header or transmitter optical bench 1108 in close proximity tothe laser 1102. These components include a plurality of electriccontacts, a pair of inductors 1118 and 1121, a co-planar waveguide 1126,and a resistor (not shown, but can be used in place of one of theinductors 1118 and 1121 in certain configurations). These inductors1118, 1121, and resistors can be characterized as passive electroniccomponents, and have less wirebond parasitics due to their proximity.Additionally, maintaining a very small temperature gradient across thecomponents, both active and passive electronic components, on the headeror transmitter optical bench 1108 (most particularly the laser 1102) tomaintain their operation is desired.

AC and DC source currents are both applied to the laser 1102. Anadvantage of the present invention is that the AC and DC currents (asrepresented by arrow 1152 and arrows 1150 in FIG. 22B and 22C,respectively) come into a single branch point proximate (or directly on)the laser 1102. Larger components make the branch point from the AC andDC sources move further from the laser. The present invention usessmaller components in more dense configurations, and has a branch pointthat converges close to the laser.

In certain embodiments, as shown in FIG. 22B, the temperature sensor1130 is positioned as close as practical (e.g., less than severalmillimeters, such as 0.6 mm) from the center of the laser 1102. It maybe desired to position the temperature sensor 1130 further away from theheader or transmitter optical bench because the header or transmitteroptical bench 1108 (on which the laser 1102 is mounted) can be verydensely populated. Positioning the temperature sensor 1130 at locationsremote from the header or transmitter optical bench 1108 still canprovide relatively reliable temperature indications, although not as onthe header or transmitter optical bench 1108. Positioning thetemperature sensor 1130 and the laser 1102 on the header or transmitteroptical bench 108 is especially important to provide accurate feedbackregarding the temperature of the laser in order to modify the AC currentand the positive DC bias current appropriately to control the opticallight output of the laser very accurately over a broad temperaturerange. In miniaturized optical devices some heat is radiated through theair from the laser 1102 to the temperature sensor 1130 howeverconvective and radiative effects are negligible as compared to thethermally conducted energy.

The thermal cross-coupling between the heat generated by the laserdriver 1104 and heat generated by the laser 1102 is limited by physicallocation. In some embodiments, some components that determine theapproximate temperature of the laser 1102 are placed within the devicepackage case 122 but not on the header or transmitter optical bench1108. In such embodiments, an offset or calibration factor approximationmust be determined to account for the thermal resistance between thelaser and the aforementioned temperature transducer. Alternatively,optical wavelength measurements can be taken over a given temperaturerange to determine laser device temperature quite accurately to verifythe accuracy of the temperature measured by the temperature sensor 1130.This procedure may not be practical for real time temperature monitoringfor certain applications.

By positioning filter elements and/or other RF components 1116 insidethe device package case 122 for the optical transmitter, the bias noiseproduced by devices external to the device package to the filterelements inside the device package is limited. Such bias noise wouldotherwise interfere with the signal quality at the laser 1102. Activelyfiltering this pseudorandom bias noise is impractical. Eye diagrams,e.g., FIG. 34 (which represent the integrity of the rise time and thefall time of the electrical signal, and can similarly be used todescribe the quality of an optical signal) indicate a compromise in theoutput of the optical transmitter resulting from any external biasnoise. In such unfilter conditions, overshoot, undershoot, ringing, andvarious types of signal abnormalities known as jitter, etc. degrade therise time and fall time and the resultant shape of the eye diagram. Inone embodiment, the filtering elements are close to the laser 1102,which allows the eye diagram to be finely tuned.

Considering the relatively small dimensions of the header or transmitteroptical bench 1108, many components positioned on the header ortransmitter optical bench 1108 are positioned within a small distance(e.g., within a few millimeters) from the laser 1102. The header ortransmitter optical bench 1108 can be produced, regardless of itscomplexity, by etching, micro-machining, plating, metal or glassdeposition, implantation or using other conventional semiconductorprocessing techniques. A mask can be used to form a large number (e.g.,sixty or more) headers or optical benches 1108 concurrently usingcurrent semiconductor processing techniques.

In one embodiment, the electrical connections to the header ortransmitter optical bench 1108 circuitry for purposes of testingsubassembly functionality are provided by so-called pogo pins (or probecontacts or testing pins) mounted onto a suitable testcard, physicallycontact the substrate at predefined locations that are selectivelyconnected. In this embodiment, after fabrication of the header assembly,a plurality of testing probes are moved toward a corresponding pluralityof contact pads on the fabricated header assembly. Electrical operationof components on the fabricated header assembly is tested after thetesting probes physically contact the contact pads. The testing probesare preferably not permanently affixed to the contact pads during thetesting procedure, but simply are in electrical contact therewith.Accordingly, the header assembly design of the present inventionrepresents a fully-testable header assembly design.

The concept of positioning passive electrical components such asinductors, capacitors, resistors, etc. on the header or transmitteroptical bench 1108 or the hybrid subassembly 1105 has been describedherein. Positioning such passive electrical components as inductors onthe same header or transmitter optical bench 1108 as the laser 1102provides unexpected results since the electronic circuit including thepassive components can be designed to operate at a high electricalfrequency or data rate. Such an integrated optical transmitter 112 oroptical transponder 100 can be applied to telecommunications, medical,computer, and other applications.

Once it is recognized that the passive electrical components could belocated inside the device package case 122 on, e.g., the header ortransmitter optical bench 1108, it might not be desired to locate thesecomponents outside the device package case 122. The physical componentsof the microwave circuit are important to provide the desiredelectro-optical operation. The components are closely positioned to thelaser 1102 on the header or transmitter optical bench 1108. In otherembodiments, these passive components are positioned remotely instead ofbeing on the header or transmitter optical bench 1108. A circuit diagramin which the passive electrical component is positioned in the devicepackage case 122 would appear similar to a circuit diagram in which thepassive electrical component is positioned outside of the device packagecase 122 if a wire extending from inside to outside the device packagecase 122 were added, but the longer length of the wire would result inproducing a larger inductor element and a resistor. The circuit diagramwould actually be different if the trace extended off the header ortransmitter optical bench 1108, or outside of the device package case122 due to the added length of such an inductor. As such, one embodimentof micro-circuit requires an inductor to be located near the laser 1102.Different lasers 1102 with different resistances and differentbandwidths can therefore be swapped along with suitable matchingresistors 1124 within the device package case 122 where it isreconfigured to provide different operational characteristics, and theheader or transmitter optical bench 1108 configuration will stillprovide improved cooling characteristics regardless of the laser 1102configuration.

In those embodiments of optical transmitter 112 where the inductor andother passive electronic components are inside the device package case122, the optical devices operate with less EMI transmitted therebetween. Positioning the electric traces 214 outside the device packagecase 122 results in a more complex design, because the circuit must beadapted to accommodate various inherent electrical parasitic elementsassociated with the longer traces and multiple laser 1102 or laserdriver 1104 designs.

IID. Heat Sinking

The laser 1102 generates approximately {fraction (7/10)} of a watt ofpower during normal operation. The heat dissipation associated with thelaser is spread downwardly through the material of the header ortransmitter optical bench 1108 as described herein. The heat sink flowthrough the optical transmitter is through the following components:laser, the header, the pedestal, the adhesive pad, and the housing case.The adhesive pad 605 secures to the baseplate 202 of the opticaltransmitter 112 within the optical transponder 100 in a position thatsinks heat downwardly from the header or transmitter optical bench 1108and/or the hybrid subassembly 1105. The header or transmitter opticalbench 1108 and the hybrid subassembly 1105 may be configured as heatspreaders. In certain embodiments, the laser driver 1104 generates morethermal energy than the laser 1102; in other embodiments the laser 1102generates more thermal energy than the laser driver 1104. Any heat flowbetween the laser 1102 and the laser driver 1104 is a function of therelative temperature of the laser 1102 and the laser driver 1104.Because of the heat transmission (e.g., 0.7 Watts) from the laser 1102through the header or transmitter optical bench 1108 and by the laserdriver 1104 (e.g., 1.5 w) through the hybrid subassembly 1105, thethermal coupling between the laser driver 1104 and the laser 1102 isintentionally limited to improve the operation of the laser 1102. Inthis embodiment, the heat generated by the laser driver 1104 does notincrease the operating temperature of the laser 1102 significantly. Thislimited thermal cross-coupling is desired since the laser 1102 operationcan be maintained within controlled temperature ranges if less externalheat is applied to the laser. The bandwidth of the laser 1102 variesinversely as a function of temperature, so reducing temperature of thelaser results in higher frequency operation because a higher laser drivecurrent can be used. If the temperature of the laser 1102 is preciselycontrolled then the bandwidth of the laser is precisely controlled. SeeFIGS. 23 and 24.

In one embodiment shown in FIGS. 17A, 22 and 27, a substantiallyvertical air trench 1134 extends between the header or transmitteroptical bench 1108 and the hybrid subassembly 1105. Air is a poorthermal conductor and as such, the air trench 1134 insulates againstheat transfer. The header or transmitter optical bench 1108, the hybridassembly 1105 and the baseplate 202 are made of different materials. Forexample, in certain embodiments, the header or transmitter optical bench1108 includes silicon, the hybrid subassembly 1105 includes aluminumnitride and the baseplate includes copper tungsten. As discussedpreviously, other material options exist. The respective layers 2720,2724, and 2728 of the pedestals 1136, 1137 as shown in FIG. 27A are madefrom materials having a generally increasing thermal conductivity as thereference character increases (though certain layers may be made from anidentical material as an adjacent layer or sub-layer). These pedestalconfigurations limit heat flow upward from the baseplate 202 via theheader or transmitter optical bench 1108 toward such heat generatingsources as the laser driver 1104 or the laser 1102. The baseplate 202,and pedestals 1136, 1137 that respectively support the hybridsubassembly 1105 and the header or transmitter optical bench 1108, whichin turn respectively support the laser driver 1104 and the laser 1102,as shown in FIG. 27, considered together and described below, act as aheat sink that dissipates heat away from the heat generating componentsmounted to the header or transmitter optical bench 1108 and the hybridsubassembly 1105.

The flow of heat away from the laser 1102 and the laser driver 1104 intothe pedestals 1136 and 1137 can be analogized to the flow of water whichnaturally flows to the lowest potential. This is the basis for Fourier'sLaw of Heat Conduction, described generally in E. Sergent and A. Krum,Thermal Management Handbook For Electronic Assemblies, at 5.5-5.7. Heatdoes not naturally flow against a thermal potential, but instead flowstoward a location (e.g., the pedestals 1136, 1137) where less thermalenergy is located. Heat generated by the laser driver 1104 flowsdownwardly through the hybrid subassembly into the device package case122 of the optical transmitter 112. From there, heat flows downwardthrough the adhesive pad 605 of the optical transmitter 112, into thepedestal 1606, and finally into the housing case 123. Less thermalenergy exists in the pedestals 1137 and 1136 than respectively in theheader or transmitter optical bench 1108 or the hybrid subassembly 1105because there are no thermal energy sources directly affixed to orwithin the pedestals. The air trench 1134 thus acts to decouple thethermal output of the laser driver 1104 from the laser 1102. Air in theair trench 1134 acts as a thermal insulator between pedestals 1136, 1137(the header or transmitter optical bench 1108 and the hybrid subassembly1105) that delineates both lateral boundaries of the air trench 1134.The pedestal 1136 that supports the laser 1102 is in one embodiment atsubstantially the same vertical height as the pedestal 1137 thatsupports the laser driver 1104. As such, the air trench 1134 issimilarly deep for both pedestals 1136 and 1137. The thermal energytherefore sinks through the pedestals 1136, 1137 toward the baseplate202. The thickness of the layers of the pedestals 1136, 1137 can varyhowever. For example, in FIG. 27, the pedestal 1136 includes one layerwhile pedestal 1137 includes two layers. In one embodiment, thepedestals 1136, 1137 are formed from copper tungsten (CuW). Thermalcross-coupling occurs at the base of the air trench 1134 but is tooremote from the laser 1102 to have a significant effect on the operationof the laser. Additionally, thermal energy in this region will flow toadjacent regions of lower potential, namely the thermal pad and thepedestal 1606.

The term “sink” normally implies that heat flows in a specific directionfrom highest to lowest thermal potential (e.g. from hot to cold). In thecase of a heat sink, moreover, thermal energy is drawn generally towardthe outside of the device package case 122 (into the baseplate 202) fromthe header or transmitter optical bench 1108 and the hybrid subassembly1105 because thermal energy flows to the lowest energy potential.Therefore, with the absence of the air trench 1134, heat would coupledirectly from the laser driver 1104 via the header or transmitteroptical bench 1108 and the hybrid subassembly 1105 to the laser 1102. Inthis embodiment, the thermal coupling would result because the laser1102 generates less thermal energy (heat) than the laser driver 1104.

To illustrate the flow of thermal energy (heat) through the header 1108,the hybrid subassembly 1105, and the pedestals 1136, 1137, thermalenergy can be modeled to follow within the shape of inverted conesdefined by Fourier's Law of Heat Conduction. In the thermal energy toflow through a series of layers 2720, 2724, and 2728 as shown in FIGS.25 and 26, heat is applied at the upper surface of the pedestals 1136,1337 (that for the purpose of this discussion includes the header 1108and the hybrid subassembly 1105), at a modeled heat generation point1140. To follow the flow of heat through the pedestal 1136, 1137 fromthe heat generation point 1140, Fourier's Law of Heat Conduction can beapplied. At each successive layer 2720, 2724, and 2728 within thepedestals 1136, 1137, thermal energy that is flowing downward within thepedestals 1136, 1137, is gradually dissipated in those areas of thelayers 2720, 2724, and 2728 that form an inverted-conical shape formedapproximately 45 degrees (i.e., 35-55 degrees) from vertical. As such,the heat-dissipating region is formed by a downward cone 1142 formedapproximately 45 degrees from vertical. This approximation assumes thatinterfacial thermal discontinuities do not exist. Where interfacialdiscontinuities do exist, horizontal heat spreading will dominate. Forexample, where the discontinuity is significant, such as a very lowthermal conductivity and/or an air-gap, the conical angle describedherein will approach 90 degrees from vertical, heat sinking through thematerial will cease and pure horizontal heat spreading will result. Thisis the case when a low thermal conductivity material is sandwichedbetween highly thermally conductive bodies. The heat sinking issuccessively repeated for each lower layer 2720, 2724, and 2728 withinthe pedestals 1136, 1137. With each lower layer, the heat is “sunk” overa wider footprint through inverted cones defined by Fourier's Law ofThermal Conduction as long as no vertical wall 1144 or other barrier isencountered. If two such heat sinking cones 1142 converge, thermalcross-coupling results. The less this merging of the heat from the heatsinking cones that is applied to raise the temperature of the header ortransmitter optical bench adjacent the laser 1102, the better thermalenergy from external sources is isolated from the laser. Due to thermalflow at the overlap of the heat sinking regions, the hotter region heatsthe cooler region. However, if a critical barrier such as the verticalwall 1144 or air trench 1134 is encountered, as shown in FIG. 26, theheat no longer follows the inverted cone as described by Fourier's Lawof Heat Conduction, but instead is constrained to follow the outline ofthe respective limiting barrier wall 1144 or air trench 1134. When theconical surface encounters a barrier wall 1144 or air trench 1134, theheat no longer propagates at approximately 45 degrees. The heat flowingwithin the material of the pedestal 1136 or 1137 reaches the edge of theair trench 1134 and thereupon saturates at the edge to form a truncatedheat dissipation region. Therefore, the pedestals 1136, 1137 do notprovide the same thermal transfer rate if the lateral area of heatdissipation is limited.

Effective heat sinking increases the performance of the layers 2720,2724 and 2728 (of the pedestals 1136, 1137), acts to lower thetemperature of the laser 1102, and thereby increases the laser'sperformance. By positioning a heat-generation source such as the laser1102 or laser driver 1104 in the middle of the pedestal 1137 (away fromany vertical wall 1144), the effectiveness of the heat sinking improves.This heat sinking improvement can be considered as equivalent toincreasing the dimensions of heat sinking cones 1142 in each pedestal1136, 1137. This increase in the dimension of the heat sinking cones1142 results in an increased horizontal cross-sectional area of thematerial of the header or transmitter optical bench 1108 that is allowedto sink heat. If the heat generation point 1140 is horizontally locatednear a vertical wall 1144 (as a result of a boundary with, e.g., an airtrench 1134), the heat sinking cone 1142 is truncated by the trench orwall. The laser 1102 is thereby positioned near the middle of thepedestal 1136 for effective heat sinking. Thermal considerations arevery critical to improve laser 1102 operation as described herein. Inone configuration, shown in FIG. 27A, the laser 1102 is positioned onthe header or transmitter optical bench such that the heat sinking conethat extends downward through the pedestal supporting the header doesnot intersect the vertical wall of air trench 1134.

The material of the header or transmitter optical bench 1108 ispartially selected to match the coefficient of thermal expansion of thelaser 1102. Due to this matching of the thermal expansion, the laser1104 does not develop cracks from internal stresses generated betweenthe laser 1104 and the header or transmitter optical bench 1108 when thetemperature of the laser 1102 cycles. The material of the hybridsubassembly 1105 is configured to match the coefficient of thermalexpansion of the material of the laser driver 1104. The hybridsubassembly 1105 is at least partially formed, in one embodiment, ofaluminum nitride, based on thermal and expansion characteristics of thematerial of the laser driver 1104. Additionally, the laser driver 1102does not develop cracks from internal stresses generated between thelaser driver 1102 and the hybrid subassembly 1105 as the temperaturecycles.

Certain components mounted on the header or transmitter optical bench1108 do not generate heat, and as such are not modeled asheat-generation points. For example, co-planar waveguides, capacitors,inductive coils and certain active integrated circuits do not generateheat. Certain resistors and transistors (not shown but common inelectronic devices), lasers 1102, and laser drivers 1104 do generateheat. Decreasing the depth of the air trench 1134 acts to increase thethermal cross-coupling between heat-generating components on thepedestals 1136, 1137 which respectively support the laser 1102 and thelaser driver 1104. In certain configurations, if the base of the airtrench 1134 is not sufficiently deep, the laser 1102 could be subjectedto increased heat exposure from thermal coupling from the laser driver1104 via the hybrid subassembly 1105 and the header or transmitteroptical bench 1108 to the laser 1102. This thermal cross-coupling mightdiminish the operating characteristics of the laser as described herein.It is therefore desired to extend the air trench 1134 lower into thesubstrate relative to the laser 1102 and the laser driver 1104, oralternatively, to increase the height of the pedestals 1136, 1137. Suchincrease in thermal cross-coupling from the laser driver 1104 via thehybrid subassembly 1105 can also be increased by selecting materialsthat have an increased heat-sinking characteristic.

For thermal and optical reasons, the laser 1102 is positioned on adifferent pedestal 1136 (that corresponds to the header or transmitteroptical bench 1108) from the pedestal 1137 (that corresponds to thehybrid subassembly 1105) on which the laser driver 1104 is positioned.Locating the laser driver 1104 in addition to the laser 1102 on theheader or transmitter optical bench 1108 would complicate the designbecause there would be a significant thermal source proximate to thelaser 1102. As such, the thermal conductivity characteristics of theheader or transmitter optical bench 1108 have not been changed and thusare not able to adequately dissipate the thermal energy for a secondheat generating device. The laser driver 1104 produces a great amount ofheat, and the heat from the laser 1102 and the laser driver 1104 wouldincrease the temperature of the laser.

There are therefore two balancing considerations: heat should be locallysunk from the laser 1102 as effectively as possible, and the thermalcoupling heat between the laser driver 1104 and the laser 1102 should belimited. Sinking heat from the laser 1102 without heat from the laserdriver 1104 being thermally coupled to the laser 1102 improves the laser1102 operating conditions. Laser 1102 operating characteristics areimproved in those applications where the laser 1102 is located in themiddle of the header or transmitter optical bench 1108, and the headeris sufficently large to satisfy unimpeded heat spreading. Small headers(e.g., 2-3 times larger than the laser surface area) or edge-mountedlasers are less able to effectively dissipate energy.

As shown in FIGS. 23-24, these heat sinking concepts are applicable to 1GHz, and are of even more concern in 1 GHz and other higher frequencysystems of that operate in the absence of thermoelectric coolers.Certain embodiments of the header or transmitter optical bench 1108supporting the laser 1102, are designed to be capable of dissipating onewatt or more of power (energy). The laser 1102, in the herein-describedembodiment, runs at a high output and at a relatively low temperatureabove the transmitter package case temperature, and yet is stilleffective. The heat sinking can be modeled using existing commerciallyavailable heat transfer computer simulation programs.

Two exemplary plotted curves, as shown in FIGS. 23 and 24, togetherillustrate how the operation of the laser 1102 is affected bytemperature. The curves 1308, 1309, 1310 as shown in FIG. 23 plotcurrent (abscissa) versus power out (ordinate) of a laser at differenttemperatures. Preferably, a steeper slope of power versus current isdesired (a higher effective temperature is detrimental to output power).FIG. 24 plots a gain-bandwidth curve in which frequency (abscissa) is.plotted versus gain (ordinate) at different electrical currents appliedto the laser.

In FIG. 24, curve 1402 shows how the gain-bandwidth of a typical laseris dependent on the amount of current applied above the thresholdcondition. Curve 1404 shows the curve for 10 milliamps above threshold(I_(th+10)). Curve 1406 shows 20 milliamps above threshold (I_(th+20)).As more current is applied, the curves extend to a higher frequencybandwidth as shown by curve 1408. The curves 1402, 1404, 1406, and 1408shown in FIG. 24 generally gradually merge as the frequency increases.Then at the some gain value particular for each curve 1404, 1406, 1408,each curve value quickly diminishes toward zero gain.

Present systems, for telecommunications lasers, presently operate at 2.5GHz at which frequency the laser operates at approximately I_(th+10)milliamps. To increase bandwidth, higher laser drive currents arerequired which in turn generates more thermal energy at the laser. At 10GHz the laser operates at I_(th+40) milliamps, for example. Therefore,it becomes even more important to dissipate sufficient heat to maintainthe laser 1102 within reasonable operating conditions.

As per FIG. 23 and 24, high bandwidth devices (e.g., 10 GHz), are oftenrequired to operate at their functional limits. Each curve 1308, 1309,1310 does not extend indefinitely, but each curve tends to “roll-over”at a point 1320 where the slope of the power-current curve is zero.Therefore, the rate of increase for output power diminishes for acorresponding increase in input current after the laser reaches itsroll-over point 1320. If the laser 1102 is driven harder by more currentbeing applied to the laser, and no more light will be projected by thelaser since the laser is outputting its maximum light, any power appliedto/from the laser 1102 that is not converted into light is convertedprimarily into heat. If more heat is applied to the laser 1102, thelaser will therefore degrade in its operation and reliability, andfollow the lower power-current curves 1308, 1309. By effectively heatsinking the laser 1102, the slope of the power-current curve that thelaser follows increases (as shown by curve 1310) to a higher power valuecurve. The heat sinking configurations described above seek to maintainthe laser 1102 at a maximum slope efficiency (power as a function ofcurrent).

The curve 1310 produces more light for a given current level thancurves, 1308 and 1309, due to the fact that the laser is operatingcooler because more heat has been drawn away from the laser 1102. Thisheat sinking allows significantly improved (e.g., 40% or more) outputpower from certain lasers 1102, when compared to standard commerciallyavailable laser-mount heat sinks. This increased output power from thelaser 1102 effectively produces more light, with less current at ahigher bandwidth because the structure concurrently sinks more heat thanconventional designs. In another embodiment, the increased heat wouldotherwise have to be dissipated by use of a thermoelectric cooler to getsimilar power-current results. As such, it is possible, with properthermal design, that high bandwidth lasers can produce more light outputwith less current without the use of active cooling techniques such asthermoelectric coolers or heatpipes.

If the laser 1102 is operating hotter, it requires more current toproduce equivalent levels of light output. As per FIG. 23, if heatsinking is poor, then the temperature of the laser increases. If theheat sinking is poor and the laser temperature increases, the slopeefficiency (which is represented by the slope of curves 1308, 1309, and1310) will decrease as represented on FIG. 23. When operating underdecreasing slope efficiencies, in order to obtain an equal amount oflight, the input current to the laser has to increase. Per Ohm'sLaws,when the laser current increases, the laser temperature increases, whichresults in a continued drop in slope efficiency. This associated loopingof the increasing current to the laser, increasing heat generated by thelaser, and increasing slope efficiency can result in a so-called“thermal runaway” condition, under which conditions, eventually thecurrent of the laser increases along the particular temperature curve1308, 1309 and 1310 until they reach the respective “roll-over” point1320 along the particular curve 1308, 1309, 1310. Continuing to applyelectric current to the lasers on a particular curve 1308, 1309, 1310where the current exceeds that of the roll-over point, will not onlyresult in diminishing light output, but may eventually damage the laser1102 itself.

Lasers that are operated at higher temperatures because of poor laserheat sinking therefore can be run only operate safely at lower outputpower for an equivalent amount of drive current, and therefore cannotreliably produce the same level of light as more efficient, better heatsinked lasers. Tests indicate the operating temperature of lasers aretypically reduced by, e.g., three to five degrees (laser operatingtemperature) by using effective passive heat sinking techniques. Thisthree to five degree reduction provided by the heat sinking describedherein can be very significant in increasing light output potential,desirable for longer transmission lengths in the optical network, andlimiting laser operational degradation, as degradation occursexponentially as temperature increases.

The low thermal resistances of the header or transmitter optical bench1108 and pedestal provide very efficient thermal design of the opticaltransmitter 112. In one embodiment, a cooler can be located external tothe device package case 122 to provide cooling. External coolers can beused rather than internal coolers that are located within the devicepackage case 122. In one embodiment, an internal cooler can beconfigured as a small thermoelectric cooler that can be applied to coolonly the mounted laser header or transmitter optical bench internal tothe package. The laser 1102 could be cooled independently from the othertechniques described herein to provide superior cooling. Positioning theexternal cooler outside of device package case 122 simplifies thepackaging design, while keeping the optical device dimensions the same;in this configuration, the cooling efficiency may decrease.

Cooling the laser 1102 becomes very important in a variety oflaser-based system where the laser operating frequency is a function ofthe temperature of the laser 1102. For a laser that is being operated ata prescribed wavelength, the electric current versus the power (andfrequency) plot can therefore more precisely be controlled as desired ifthe temperature of the laser is precisely monitored and controlled. Oneapplication using multiple lasers that in which each are preciselyindividually controlled is wavelength division multiplexing (WDM)systems. Such WDM systems utilize a plurality of lasers, each laseroperating at a slightly different wavelength (color), and the differentdata streams output by all of the lasers are merged in the same opticalfiber cable 120. It therefore becomes even more essential to ensure thatthe output wavelength of the light is very tightly controlled. Eachlaser is very tightly monitored and controlled, so the differentwavelengths of light produced by each distinct laser is stable over abroad temperature range. All the lasers have to be cooled/heated totheir particular fixed operating temperature. To achieve thiscooling/heating, a wavelength photo monitor 1114 can monitor the outputof each laser 1102. To provide multiple lasers 1102 in the same devicepackage case 122, the lasers 1102 must be cooled/heated very accuratelyand independently. Again, the temperature sensor 1130 may be positionedon the header or transmitter optical bench 1108. With dense wavelengthdivision multiplexing (DWDM), the temperature of each laser 1102 has tobe very accurately controlled over its active life. Thus, a laser 1102producing a specific wavelength (e.g., 1550 nm) may be necessary toachieve proper operation in certain operations.

If it is desired to integrate a component (e.g., a co-planar waveguide)into silicon patterning, high-resistivity silicon is necessary. Ahigh-resistivity silicon could cost considerably more than alow-resistivity material. For comparison purposes, a high-resistivitysilicon might cost five to ten times as much as low-resistivity silicon.The low resistivity silicon makes the silicon more economically feasiblefor a broader base of products. The optical transmitter 112 and opticaltransponder 100 utilizing low-resistivity silicon may be desired formany applications because it does not have the cost associated with highresistivity silicon. The thermal conductivity of doped silicon isindistinguishable from that of non-doped silicon, because the dopant isso subtle.

Metal filled vias (not shown in this embodiment) may be used in theembodiment of hybrid assembly 1105, and may be made from alumina, toremove the heat generated by the laser driver 1104, and other heatgenerating components. The vias in the alumina configuration of thehybrid assembly 1165 extend straight down to the baseplate 202, so thedissipated heat travels down within the vias in which there is a morelimited area to dissipate heat than the embodiment shown in the ceramiclayers 2720, 2724, and 2728 of FIG. 27. Thus vias would not be aseffective for heat dissipation as the aluminum nitride included in thehybrid assembly 1105 described above because of the limited spreadingeffect. The heat cannot spread laterally from the small area defined bythe vias. From a thermal density point of view, the vias 218 of thealumina embodiment of the hybrid assembly 1105 act like a thermal chokelimited by vertical conduction with very little horizontal heatspreading.

The embodiment of hybrid subassembly 1105 formed from aluminum nitride,by comparison, has good heat coefficient properties and thus provides animproved thermal sinking and spreading effect. Similar results could beachieved with the header or transmitter optical bench 1108 being formedfrom silicon carbide, beryllium oxide, sapphire or diamond. Diamondheaders 1108 are not commonly used for economic reasons and berylliumoxide is not frequently used because of toxicity hazards. The heatsinking aspects described above are also applicable to other portions ofthe transponder 100. For example, an air trench 1134 can be formedbetween whichever pair of elements generate considerable heat. In FIG.17A, the air trench 1134 is formed between the pedestal 1606 supportingthe optical receiver 114 and the pedestal 1606 supporting the opticaltransmitter 112. By comparison, an air trench 1134 can be providedbetween the pedestal 256 supporting an electrical demultiplexer 252 anda pedestal 1606 supporting the optical receiver 114 as shown in theembodiment of FIG. 17B. The selection of which pair, or pairs, of heatgenerating components to position an air trench between depends largelyon selecting those pairs of components that are generating the most heatwithin the optical transponder 100. For instance, in certain transponderconfigurations, the electrical demultiplexer 252 and the opticalreceiver may generate the most heat.

IIE. Optical Isolators

FIG. 35 illustrates an optical isolator. The purpose of opticalisolators, in general, is to act as optical diodes to allow light totravel in a first direction, while limiting the transmission of light ina second direction, that is opposed from the first direction. As such,magnetic fields maybe applied to the optical element 3606 by magneticpolar sources 3604. Magnet fields affect the polarization of the opticalelement, thereby affecting whether the optical isolator allows light topass through the optical element.

Light can travel within the optical isolator 3600 in a directiongenerally parallel to, or slightly angled from, the optical element axis3804. The optical isolator 3600 is configured so that light from alaser, such as 1102 shown in FIG. 22A, can be directed therethrough. Iflight emitted from the laser 1102 is reflected from the optical isolator3600 back to the laser, degredation can result to the optical signal. Assuch, the optical element axis 3804 is configured at an angle, so thatnone of the incident light from the laser that is reflected off of thesurface of the first optical element, reflects back toward the laser. Assuch, any light emitted from the laser 1102, which the contacts theoptical element 3606 will typically pass through the optical element,however, any light that is reflected from the optical element will notbe reflected back to the laser.

As shown in FIG. 35, each one of a plurality of magnetic polar sources3604 has its own magnet axis 3802. Each magnetic polar source 3604 has alength (L1) that extends beyond the length (L2) of the optical element3606. The optical element 3606 has a central or optical element axis3804. The optical element axis 3804 is tilted with respect to each ofthe magnet axis 3802, at an angle of 2-12 degrees. The length (L1) ofthe magnetic polar sources 3604 taken in a direction along the magnetaxis 3802, is elongated compared to the length (L2) of the opticalelement 3606 as taken in the direction parallel to the magnet axis 3802.The magnets 3604 are of sufficient length to extend past the edge of themounting substrate 3540. As such, the magnets have an overhang portion3520. The overhang portion 3520 has a mounting substrate 3540 that issufficiently planer to provide for a mounting against a planer surfaceof the interior of the housing case 122. Such elongation of the magnets3802 relative to the optical element 3606 provides the ability toposition the optical isolator 3600 with housing case 122 simply byplacement of the optical isolator 3600 along the inner surface ofhousing case 122. Without the overhang portions 3520, the magneticelements 3604 could not come in direct contact with the planer surfaceof the interior of the housing case and the structure would tilt out ofposition.

Another embodiment of optical isolator 3600 is shown in FIGS. 36 and 37.The optical isolator 3600 includes a single U-shaped magnet 3640. TheU-shaped magnet 3640 has a first magnetic polar source 3642 (e.g., a“north pole”), a second magnetic polar source (e.g., a “south pole”)3644, and a connector segment 3650. The optical element 3606 isconnected to the connector segment 3650 by any fasten method such asadhesive, epoxy, solder, mechanical connector, or the like. The firstmagnetic polar source 3642 and the second magnetic polar source 3644each have their individual pole source axis 3646. The optical elementaxis 3804 is tilted from 2 to 12 degrees from each magnetic polar sourceaxis 3646, to limit the light from the laser being reflected back towardthe laser (as described relative to the embodiment shown in FIG. 35).The length L1 of the magnetic polar sources 3642, 3644 exceeds thelength L2 of the optical element 3606.

The U-shaped magnet 3640 has a substantially planer mounting surface3650, formed from a substantially planer edge of the U-shaped magnet3640. The housing case 123 of the optical transmitter 112 (and/or acomponent connected thereto) includes magnetically attractive materialof sufficient strength to semi-permanently secure the optical isolator3600 relative to the housing case 123.

In one embodiment of optical transmitter 112, as shown in FIG. 22, theoptical isolator 3600 is shown as being secured to the housing case 123by magnetic attraction between the magnets 3604 of the optical isolatorand the housing case 123. The housing case 123 includes a magneticallyattractive component, such as the transmitter package wall 208 beingformed from such magnetically attractive material as Kovar. The mountingprovides a strong magnetic attraction to the magnets 3604 that is byitself sufficient to maintain the optical isolator 3600, and theassociated optical element 3606, at its desired location after placementof the optical element 3606 during assembly. This strength issufficiently strong to maintain the optical isolator in position duringnormal operation of the optical transmitter. For more robustreliability, the isolator could be permanently affixed (e.g., bysoldering, adhesive or some mechanical fixture.)

II.F. Reconfigurable Header

FIG. 31 shows one embodiment of an n-doped laser substrate structure3100, while FIG. 32 shows one embodiment of a p-doped laser substratestructure 3200. The n-doped laser substrate structure 3100 and thep-doped laser substrate structure 3200 differ from each other primarilyby their anode and cathode assignments are opposite. The embodiments ofthe laser substrate structures 3100, 3200 shown in FIGS. 31 and 32 areintended to be illustrative in nature, while it is to be understood thatother configurations of lasers may be used while remaining within theintended scope of the present invention.

Not only does the doping of the n-doped laser substrate structure 3100differ from that of the p-doped laser substrate structure 3200, but toprovide proper operation, the biasing applied to the laser substratestructures 3100, 3200 must differ as well. For example, dependent on thelaser substrate structure, different current sources are connected atdifferent locations to the different portions of the laser substratestructure.

The n-doped laser substrate structure 3100, as shown in FIG. 31,includes a base anode electric contact 3102, and n-substrate 3104, anactive region 3106, a p-semiconductor layer 3108, and a laser cathodeelectric contact 3110. To properly bias the n-doped laser substratestructure 3100, a DC positive bias electric current source 3112 isapplied to the base anode electric contact 3102, a modulated electric(AC) current source 3114 is also electrically connected to the baseanode electric contact 3102, and a DC negative current source 3116 iselectrically connected to the laser cathode electric contact 3110. TheDC positive bias electric current source 3112, the modulated electric(AC) current source 3114, and the DC negative electric current source3116 are electrically connected at remote electrically sources by wireor ribbon bonds. Wire or ribbon bonds are used to connect the variouscurrent sources to their respective location on the laser cathodeelectric contact 3110 or the base anode electric contact 3112.

The p-doped laser substrate structure 3200, as shown in FIG. 32,includes a base cathode electric contact 3202, a p-substrate 3204, anactive region 3206, an n-semiconductor layer 3208, and a laser anodeelectric contact 3210. The lasing action is produced within the activeregion 3206, in a similar manner to lasing action being produced in theactive region 3106 of the n-doped laser substrate structure 3100. Toproperly bias the p-doped laser substrate structure 3200, the modulatedelectric (AC) current source 3114 is electrically connected to the laseranode electric contact 3210, the DC positive bias electric currentsource 3112 is electrically connected to the laser anode electriccontact 3210, and the DC negative current source 3116 is electricallyconnected to the base cathode electric contact 3202.

The embodiment of reconfigurable laser header 3302, as shown in FIGS.33A or 33B is used in such a manner that a laser 3304 (whether it is ap-doped laser substrate structure 3200 as shown in FIG. 32, or a n-dopedlaser substrate structure 3100 as shown in FIG. 31) may be properlybiased. The reconfigurable laser header assembly 3302 is shown in FIG.33A in its configuration to bias a p-doped laser substrate structure3200, and is shown in FIG. 33B in its configuration to bias an n-dopedlaser substrate structure 3100. The reconfigurable laser header assembly3302 includes, in one embodiment, a header 3306, the laser 3304, anelectric conductor 3308, the bias DC positive electric current source3112, the DC negative current source 3116, and the modulated electric(AC) current source 3114. The header 3306 is provided to support thelaser 3304. The electrical conductor 3308 extends around the peripheryof the laser 3304, and is electrically connected to the base electriccontact 3102 of laser 3304. In FIG. 33A, the base electric contact 3202may be considered as extending around the periphery at the base of thelaser 3200. In FIG. 33B, the base electric contact 3102 may beconsidered as extending around the periphery of the base of the laser3100.

The electrical conductor 3308 may be patterned on the header or siliconoptical bench 3306. The header or transmitter optical bench may be madeout of any suitable material, including, but not limited to, silicon,aluminum nitrate (AIN), or silicon carbide (SiC), diamond or sapphire.

In one embodiment, the electrical conductor 3308 includes a firstmetalized region 3316 and a second metalized region 3318. The selectionof which metalized region is characterized as the first metalized region3316 or the second metalized region 3318 determines the lasingorientation of the laser. The actual structure of both metalized regionsare preferably identical, but located on opposite sides of the laser3304. The electrical conductor 3308 further includes a pair ofconnecting electrical conductors 3120 that electrically connect thefirst metalized region 3316 to the second metalized region 3318. Theconnecting electrical conductors 3120 extend around opposed sides of thelaser 3304, as illustrated in FIG. 33A and 33B.

As mentioned, the reconfigurable laser header assembly 3302 may be usedto properly electrically bias the laser 3304 regardless of whether thelaser 3304 is a p-doped laser substrate structure 3200, as shown in FIG.32, or an n-doped laser substrate structure 3100, as shown in FIG. 31.To accomplish this biasing of the p-doped laser substrate structure3200, as shown in FIG. 33A, a first set of wire bonds 3320 are connectedfrom a variety of current sources to a variety of locations relative tothe laser substrate structure 3200. In this disclosure, the term “wirebond” may include any wire bond, ribbon bond, or other wire or conductorthat electrically connects the two locations as described herein. Afirst wire bond 3320 extends from the DC positive electric currentsource 3112 to the laser anode electric contact 3210. A second wire bond3320 extends from the modulated electric (AC) current source 3114 to thelaser anode electric contact 3210. A third one of the wire bonds 3320extends from one or more of the DC negative current source 3116 to thesecond metalized region 3318 (alternatively, the first metalized region3316).

In those instances where the laser 3304 is an n-doped laser substratestructure 3100, as illustrated in FIG. 31, the biasing of thereconfigurable laser header assembly 3302 is different as shown in FIG.33B. One second wire bond 3322 extends from the DC positive biaselectric current source 3112 to the metalized region 3316(alternatively, the second electrical metalized region 3318). Anothersecond wire bond 3322 extends from one or more of the DC negativeelectric source 3316 to the laser cathode electric contact 3310. Anothersecond wire bond 3322 extends from the modulated electric (AC) currentsource 3114 to the second metalized region 3318 (or alternatively, thefirst metalized region 3316).

II.G. Performance Characteristics

The integration of components on the optical header and the heat sinkingaspects described above result in an optical transmitter havingsubstantially improved operating characteristics. An eye diagram of anoptical transmitter operating in accordance with the present inventionis shown in FIG. 34. As illustrated by that figure, the opticaltransmitter of the present invention exhibits a “wide open” eye, has lowovershoot, and a high mask margin at high extinction ratios.Significantly, at higher temperatures, the eye integrity of the lightproduced by the laser is maintained. The proximity of the temperaturesensor to the laser on the header as described above contributes tobetter control of the laser, and enhanced performance of the laser attemperatures approaching the roll over point.

Another important feature of certain embodiments of the opticaltransmitter described above, is the absence of any thermo-electriccooler from the device. A thermo-electric cooler will typically havesignificant power requirements, and the addition of a thermo-electriccooler to an optical transmitter may in some cases double the powerrequired to operate the device. The optical transmitter of the presentinvention is able to achieve an eye diagram having a “wide open” eye athigh operating temperatures, even in the absence of any thermoelectriccooler. This result is based in large part on the heat sinkingmethodology employed in connection with the device, as well as precisetemperature control over the laser.

Table I below illustrates that the optical transmitter of the presentinvention is able to continue operating without degradation ofperformance with low differentials between the laser temperature on theone hand, and the temperatures of the housing case (T1) and thetransmitter package case (T2). The locations on the device wheretemperatures T1, T2 are measured, are shown respectively on FIG. 27B.

TABLE I Maximum Laser Maximum Transponder Maximum Transmitter OperatingHousing Case Package Case Temperature Temperature (T1) Temperature (T2)Prior Art 75° C. 55-60° C. 65-70° C. Invention 75° C. 70° C. 74° C.

As shown in Table I, the optical transmitter of the present inventioncan achieve a 5° C. temperature delta between the laser temperature andthe housing case temperature without degradation of the operation of thedevice. In particular, when the optical transmitter of the presentinvention is configured using a laser that operates in the range of1260-1360 nm, and the transmitter package case is made small such thatit that either (i) covers less than 0.30 square inches of surface areaon a surface to which the package case is mounted, or (ii) is less than0.062 cubic inches in volume, the optical transmitter continues tofunction in compliance with the transmission requirements ofInternational Telecommunciations Union (ITU-T) Standard G.693 and/orG.691, the Synchronous Optical Network Transport System (SONET/SDH)Standard STM-64 and/or the SONET Standard OC-192, without thermoelectriccooling, when the thermal resistance of the transmitter package is lessthan or equal to 0.7 degrees C. per Watt and an external temperature ofthe functioning transmitter package case is at or within 1° C. of atemperature of the laser, and/or when the thermal resistance of thehousing case is less than or equal to 1.1 degrees C. per Watt and theexternal temperature of the functioning housing case is at or within 5°C. of a temperature of the laser. In addition, these small temperaturedeltas can be maintained when the optical transmitter is operatingcontinuously (e.g., for days or weeks on end) to transmit data atfrequencies at or above 2.5 Gbit, with an output power of at least 5dBm, and with the laser operating at a duty cycle of at least 50% orbetter. In some embodiments, the housing case is 3 inches long ×2.0inches wide ×0.53 inches thick, or 3 inches long ×2.0 inches wide ×0.53inches thick, or smaller.

While the principles of the invention have been described above inconnection with the specific apparatus and associated method, it is tobe clearly understood that this description is made only by way ofexample and not as a limitation on the scope of the invention.

What is claimed is:
 1. A reconfigurable laser header assembly, whereineither an n-doped laser substrate or a p-doped laser substrate can beproperly biased, the reconfigurable laser header assembly comprising: aheader coupled to a modulated AC electric current source, a DC positivebias electric current source, and a DC negative electric current source;an electrical conductor on the header including first and secondmetalized regions; and a laser of the type selected from the groupconsisting of an n-doped laser substrate, and a p-doped laser substrate;wherein the n-doped laser substrate includes: an n-substrate with a baseanode contact, and a p-semiconductor layer with a laser cathode contact;wherein the p-doped laser substrate includes a p-substrate with a basecathode contact, and an n-semiconductor layer with a laser anodecontact; wherein the electrical conductor is electrically connected tothe base anode contact of the n-doped laser substrate or to the basecathode contact of the p-doped laser substrate, wherein the modulated ACelectric current source and the DC positive bias electric current sourceare electrically connected to the laser anode contact with firstrelocatable conductors or to the base anode contact via the firstrelocatable conductors electrically connected to the first and/or secondmetalized regions; and wherein the DC negative electric current sourceis electrically connected to the laser cathode contact with a secondrelocatable conductor or to the base cathode contact via the secondrelocatable conductor electrically connected to the first and/or thesecond metalized regions; whereby the laser is properly biasedregardless of whether the laser is an n-doped laser substrate structureor a p-doped laser substrate structure.
 2. The reconfigurable laserheader assembly of claim 1, wherein the first and second metalizedregions are electrically connected to the base anode contact or the basecathode contact at positions approximately one hundred and eightydegrees from each other.
 3. The reconfigurable laser header assembly ofclaim 1, wherein the first and second metalized regions are supported bythe header.
 4. The reconfigurable laser header assembly of claim 1,wherein the first and second metalized regions are mounted on the laserheader.
 5. The reconfigurable laser header assembly of claim 1, furtherincluding a connecting electrical conductor that electrically connectsthe first and second metalized regions.
 6. The reconfigurable laserheader assembly of claim 5, wherein the connecting electrical conductorincludes a plurality of electrical conductors, two of the plurality ofelectrical conductors extending around opposed sides of the laser. 7.The reconfigurable laser header assembly of claim 1, wherein the laseris a p-doped laser substrate structure, wherein the first and secondrelocatable conductors include a plurality of wire bonds, wherein afirst wire bond extends from the modulated AC electric current source tothe laser anode contact, wherein a second wire bond extends from the DCpositive bias electric current source to the laser anode contact, andwherein a third wire bond extends from the DC negative electric currentsource to the first metalized region.
 8. The reconfigurable laser headerassembly of claim 1, wherein the laser is an n-doped laser substratestructure, wherein the relocatable conductors include a plurality ofwire bonds, wherein a first wire bond extends from the modulated ACelectric current source to the first metalized region, wherein a secondwire bond extends from the DC positive bias electric current source tothe second metalized region, and wherein a third wire bond extends fromthe DC negative electric current source to the laser cathode contact. 9.A method for biasing either an n-doped laser substrate structure or ap-doped laser substrate structure mounted on a laser header, the methodcomprising: a) providing a modulated AC electric current source, a DCpositive bias electric current source, and a DC negative electriccurrent source; b) mounting an electrical conductor including a firstand second metalized regions onto the laser header; c) mounting ap-doped or an n-doped laser substrate structure onto the electricalconductor, the p-doped laser substrate structure including a p-substratewith a base cathode contact and an n-semiconductor layer with a laseranode contact, the n-doped laser substrate structure including ann-substrate with a base anode contact and a p-semiconductor layer with alaser cathode contact; d) electrically connecting both the modulated ACelectric current source and the DC positive bias electric current sourceto the laser anode contact with relocatable conductors or to the baseanode contact via relocatable conductors electrically connected to thefirst and/or the second metalized regions, and e) electricallyconnecting the DC negative electric current source to the laser cathodecontact with a relocatable conductor or to the base cathode contact viaa relocatable conductor electrically connected to the first and/or thesecond metalized region, wherein the laser substrate structure isproperly biased regardless of whether the laser is an n-doped lasersubstrate structure of a p-doped laser substrate structure.
 10. Themethod of claim 9, wherein the first and second metalized regions areelectrically connected to the base anode contact or the base cathodecontact at positions approximately one hundred and eighty degrees fromeach other.
 11. The method of claim 9, wherein the first and secondmetalized regions are supported by the laser header.
 12. The method ofclaim 9, wherein the first and second metalized regions are mounted onthe laser header.
 13. The method of claim 9, further including providinga connecting electrical conductor that electrically connects the firstand second metalized regions.
 14. The method of claim 13, wherein theconnecting electrical conductor includes two electrical conductorsextending around opposed sides of the laser.
 15. The method of claim 9,wherein: step c includes mounting an n-doped laser substrate structureonto the electrical conductor; step d) includes electrically connectinga first wire bond from the modulated AC electric current source to thefirst metalized region; step d) includes electrically connecting asecond wire bond from the DC positive bias electric current source tothe second metalized region; step e) includes electrically connecting athird wire bond from the DC negative electric current source to thelaser cathode contact.
 16. The method of claim 9, wherein: step cincludes mounting a p-doped laser substrate structure onto theelectrical conductor; step d) includes electrically connecting a firstwire bond from the modulated AC electric current source to the laseranode contact; step d) includes electrically connecting a second wirebond from the DC positive bias electric current source to the laseranode contact; step e) includes electrically connecting a third wirebond from the DC negative electric current source to the first metalizedregion.